ocda, improve doc markup structure error messages

- ocda, metadoc_from_src
  workon doc markup structure error message, check

3 files changed, 1001 insertions, 221 deletions

diff --git a/flake.lock b/flake.lock
index 27adeaf..19189dc 100644
--- a/flake.lock
+++ b/flake.lock
@@ -20,11 +20,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1688894907,
-        "narHash": "sha256-U7hEDDhzAhLp6T+DEUbfwAsL+BtqFFGn+S1pa/0XrZY=",
+        "lastModified": 1688956120,
+        "narHash": "sha256-7geHGr2aLpQvwGgaZlTLPHMVFxvFzAuB35mZYsKgLpQ=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "4ddf98349c793377c76806ebfbdfb2b96dd4ef5d",
+        "rev": "2169d3b0bce0daa64d05abbdf9da552a7b8c22a7",
         "type": "github"
       },
       "original": {
diff --git a/org/ocda.org b/org/ocda.org
index 1750549..46dc72c 100644
--- a/org/ocda.org
+++ b/org/ocda.org
@@ -110,8 +110,7 @@ template docAbstraction() {
       }                                                                         // close after non code, other blocks or regular text
       <<abs_in_loop_body_reloop_get_prior_state>>
     }                                                                           /+ ← srcDocLoop closed: loop markup document/text line by line +/
-                                                                                /+ ↓ post loop markup document/text +/
-                                                                                /+ ↓ post loop markup document/text +/
+    /+ ↓ post loop markup document/text +/
     <<abs_loop_body_exit_eof_xml_dom_tail>>
     <<abs_post_endnote_tuple>>
     <<abs_post_glossary_nugget>>
@@ -910,14 +909,13 @@ debug (substitutions) {
 #+NAME: abs_in_loop_body_00_0
 #+BEGIN_SRC d
 /+ scope +/
-scope(exit) {
-}
+scope(exit) { }
 scope(failure) {
   stderr.writefln(
-    "%s\n%s\n%s:%s failed here:\n  line: %s",
+    "\n%s\n%s\n\n%s:%s\nFAILED while processing the file: ❮❮ %s ❯❯ on line with text:\n%s\n",
     __MODULE__, __FUNCTION__,
     __FILE__, __LINE__,
-    line,
+    manifested.src.filename, line,
   );
 }
 debug(source) {
@@ -925,10 +923,7 @@ debug(source) {
 }
 debug(srclines) {
   if (!line.empty) {
-    writefln(
-      "* %s",
-      line
-    );
+    writefln("* %s", line);
   }
 }
 #+END_SRC
@@ -5180,7 +5175,7 @@ if (pith["block_is"] == eN.blk_is.quote) {
     }
     an_object[an_object_key] ~= line ~= "\n";
     an_object["lev"] ~= m.captures[1];
-    assertions_doc_structure(an_object, lv); // includes most of the logic for collapsed levels
+    assertions_doc_structure(an_object, an_object_key, lv); // includes most of the logic for collapsed levels
     switch (an_object["lev"]) {
     case "A":                                // Title set
       if ((an_object[an_object_key].match(rgx.variable_doc_title_author_date))
@@ -7768,173 +7763,568 @@ invariant() {
 #+BEGIN_SRC d
 @safe pure void assertions_doc_structure()(
   string[string]  an_object,
+  string          an_object_key,
   int[string]     lv
 ) {
+  string msg_error_doc_struct = "\nERROR in document structure, check markup (heading level relationships):\n";
   if (lv["h3"] > eN.bi.off) {
-    assert(lv["h0"] > eN.bi.off);
-    assert(lv["h1"] > eN.bi.off);
-    assert(lv["h2"] > eN.bi.off);
+    assert(lv["h0"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h1"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h2"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   } else if (lv["h2"] > eN.bi.off) {
-    assert(lv["h0"] > eN.bi.off);
-    assert(lv["h1"] > eN.bi.off);
-    assert(lv["h3"] == eN.bi.off);
+    assert(lv["h0"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h1"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h3"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   } else if (lv["h1"] > eN.bi.off) {
-    assert(lv["h0"] > eN.bi.off);
-    assert(lv["h2"] == eN.bi.off);
-    assert(lv["h3"] == eN.bi.off);
+    assert(lv["h0"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h2"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h3"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   } else if (lv["h0"] > eN.bi.off) {
-    assert(lv["h1"] == eN.bi.off);
-    assert(lv["h2"] == eN.bi.off);
-    assert(lv["h3"] == eN.bi.off);
+    assert(lv["h1"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h2"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h3"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   } else {
-    assert(lv["h0"] == eN.bi.off);
-    assert(lv["h1"] == eN.bi.off);
-    assert(lv["h2"] == eN.bi.off);
-    assert(lv["h3"] == eN.bi.off);
+    assert(lv["h0"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h1"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h2"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h3"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   }
   if (lv["h7"] > eN.bi.off) {
-    assert(lv["h4"] > eN.bi.off);
-    assert(lv["h5"] > eN.bi.off);
-    assert(lv["h6"] > eN.bi.off);
+    assert(lv["h4"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ "missing segment level 1~\n"
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h5"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h6"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   } else if (lv["h6"] > eN.bi.off) {
-    assert(lv["h4"] > eN.bi.off);
-    assert(lv["h5"] > eN.bi.off);
-    assert(lv["h7"] == eN.bi.off);
+    assert(lv["h4"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ "missing segment level 1~\n"
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h5"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h7"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   } else if (lv["h5"] > eN.bi.off) {
-    assert(lv["h4"] > eN.bi.off);
-    assert(lv["h6"] == eN.bi.off);
-    assert(lv["h7"] == eN.bi.off);
+    assert(lv["h4"] > eN.bi.off,
+      msg_error_doc_struct
+      ~ "missing segment level 1~\n"
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h6"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h7"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   } else if (lv["h4"] > eN.bi.off) {
-    assert(lv["h5"] == eN.bi.off);
-    assert(lv["h6"] == eN.bi.off);
-    assert(lv["h7"] == eN.bi.off);
+    assert(lv["h5"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h6"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h7"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   } else {
-    assert(lv["h4"] == eN.bi.off);
-    assert(lv["h5"] == eN.bi.off);
-    assert(lv["h6"] == eN.bi.off);
-    assert(lv["h7"] == eN.bi.off);
+    assert(lv["h4"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ "missing segment level 1~\n"
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h5"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h6"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h7"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   }
   if (lv["h0"] == eN.bi.off) {
-    assert(lv["h1"] == eN.bi.off);
-    assert(lv["h2"] == eN.bi.off);
-    assert(lv["h3"] == eN.bi.off);
-    assert(lv["h4"] == eN.bi.off);
-    assert(lv["h5"] == eN.bi.off);
-    assert(lv["h6"] == eN.bi.off);
-    assert(lv["h7"] == eN.bi.off);
+    assert(lv["h1"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h2"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h3"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h4"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ "missing segment level 1~\n"
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h5"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h6"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h7"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   }
   if (lv["h1"] == eN.bi.off) {
-    assert(lv["h2"] == eN.bi.off);
-    assert(lv["h3"] == eN.bi.off);
+    assert(lv["h2"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h3"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   }
   if (lv["h2"] == eN.bi.off) {
-    assert(lv["h3"] == eN.bi.off);
+    assert(lv["h3"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   }
   if (lv["h3"] == eN.bi.off) {
   }
   if (lv["h4"] == eN.bi.off) {
-    assert(lv["h5"] == eN.bi.off);
-    assert(lv["h6"] == eN.bi.off);
-    assert(lv["h7"] == eN.bi.off);
+    assert(lv["h5"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h6"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h7"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   }
   if (lv["h5"] == eN.bi.off) {
-    assert(lv["h6"] == eN.bi.off);
-    assert(lv["h7"] == eN.bi.off);
+    assert(lv["h6"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
+    assert(lv["h7"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   }
   if (lv["h6"] == eN.bi.off) {
-    assert(lv["h7"] == eN.bi.off);
+    assert(lv["h7"] == eN.bi.off,
+      msg_error_doc_struct
+      ~ an_object[an_object_key]
+    );
   }
   if (lv["h7"] == eN.bi.off) {
   }
   switch ((an_object["lev"]).to!string) {
   case "A":
     if (lv["h0"] == eN.bi.off) {
-      assert(lv["h1"] == eN.bi.off);
-      assert(lv["h2"] == eN.bi.off);
-      assert(lv["h3"] == eN.bi.off);
-      assert(lv["h4"] == eN.bi.off);
-      assert(lv["h5"] == eN.bi.off);
-      assert(lv["h6"] == eN.bi.off);
-      assert(lv["h7"] == eN.bi.off);
+      assert(lv["h1"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level A~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level A~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level A~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h4"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~\n"
+        ~ "at level A~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level A~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level A~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level A~\n"
+        ~ an_object[an_object_key]
+      );
     } else {                       // (lv["h0"] > eN.bi.off)
-      assert(lv["h0"] == eN.bi.off,"error should not enter level A a second time");
+      assert(lv["h0"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "should not enter level A a second time\n"
+        ~ "at level A~\n"
+        ~ an_object[an_object_key]
+      );
     }
     break;
   case "B":
     if (lv["h1"] == eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h2"] == eN.bi.off);
-      assert(lv["h3"] == eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level B~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level B~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level B~\n"
+        ~ an_object[an_object_key]
+      );
     } else {                       // (lv["h1"] > eN.bi.off)
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h1"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level B~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h1"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level B~\n"
+        ~ an_object[an_object_key]
+      );
     }
     break;
   case "C":
     if (lv["h2"] == eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h1"] > eN.bi.off);
-      assert(lv["h3"] == eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level C~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h1"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "level C should not follow level A\n"
+        ~ "at level C~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level C~\n"
+        ~ an_object[an_object_key]
+      );
     } else {                       // (lv["h2"] > eN.bi.off)
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h1"] > eN.bi.off);
-      assert(lv["h2"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level C~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h1"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level C~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level C~\n"
+        ~ an_object[an_object_key]
+      );
     }
     break;
   case "D":
     if (lv["h3"] == eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h1"] > eN.bi.off);
-      assert(lv["h2"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level D~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h1"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "level D should not follow level A\n"
+        ~ "at level D~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level D~\n"
+        ~ an_object[an_object_key]
+      );
     } else {                      // (lv["h3"] > eN.bi.off)
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h1"] > eN.bi.off);
-      assert(lv["h2"] > eN.bi.off);
-      assert(lv["h3"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level D~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h1"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level D~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level D~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level D~\n"
+        ~ an_object[an_object_key]
+      );
     }
     break;
   case "1":
     if (lv["h4"] == eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 1~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 1~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 1~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 1~\n"
+        ~ an_object[an_object_key]
+      );
     } else {                      // (lv["h4"] > eN.bi.off)
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h4"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 1~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~ ?\n"
+        ~ "at level 1~\n"
+        ~ an_object[an_object_key]
+      );
     }
     break;
   case "2":
     if (lv["h5"] == eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h4"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 2~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~ ?\n"
+        ~ "at level 2~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 2~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 2~\n"
+        ~ an_object[an_object_key]
+      );
     } else {                      // (lv["h5"] > eN.bi.off)
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h4"] > eN.bi.off);
-      assert(lv["h5"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 2~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~ ?\n"
+        ~ "at level 2~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 2~\n"
+        ~ an_object[an_object_key]
+      );
     }
     break;
   case "3":
     if (lv["h6"] == eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h4"] > eN.bi.off);
-      assert(lv["h5"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 3~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~ ?\n"
+        ~ "at level 3~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 2~ ?\n"
+        ~ "at level 3~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 3~\n"
+        ~ an_object[an_object_key]
+      );
     } else {                      // (lv["h6"] > eN.bi.off)
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h4"] > eN.bi.off);
-      assert(lv["h5"] > eN.bi.off);
-      assert(lv["h6"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 3~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~ ?\n"
+        ~ "at level 3~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 3~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 3~\n"
+        ~ an_object[an_object_key]
+      );
     }
     break;
   case "4":
     if (lv["h7"] == eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h4"] > eN.bi.off);
-      assert(lv["h5"] > eN.bi.off);
-      assert(lv["h6"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 4~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~ ?\n"
+        ~ "at level 4~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 2~ ?\n"
+        ~ "at level 4~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 3~ ?\n"
+        ~ "at level 4~\n"
+        ~ an_object[an_object_key]
+      );
     } else {                      // (lv["h7"] > eN.bi.off)
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h4"] > eN.bi.off);
-      assert(lv["h5"] > eN.bi.off);
-      assert(lv["h6"] > eN.bi.off);
-      assert(lv["h7"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 4~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~ ?\n"
+        ~ "at level 4~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 4~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 4~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "at level 4~\n"
+        ~ an_object[an_object_key]
+      );
     }
     break;
   default:
diff --git a/src/doc_reform/meta/metadoc_from_src.d b/src/doc_reform/meta/metadoc_from_src.d
index 3962beb..59cbc0b 100644
--- a/src/doc_reform/meta/metadoc_from_src.d
+++ b/src/doc_reform/meta/metadoc_from_src.d
@@ -610,14 +610,13 @@ template docAbstraction() {
     foreach (line; markup_sourcefile_content) {                                 /+ ↓ markup document/text line by line +/
                                                                                 // "line" variable can be empty but should never be null
       /+ scope +/
-      scope(exit) {
-      }
+      scope(exit) { }
       scope(failure) {
         stderr.writefln(
-          "%s\n%s\n%s:%s failed here:\n  line: %s",
+          "\n%s\n%s\n\n%s:%s\nFAILED while processing the file: ❮❮ %s ❯❯ on line with text:\n%s\n",
           __MODULE__, __FUNCTION__,
           __FILE__, __LINE__,
-          line,
+          manifested.src.filename, line,
         );
       }
       debug(source) {
@@ -625,10 +624,7 @@ template docAbstraction() {
       }
       debug(srclines) {
         if (!line.empty) {
-          writefln(
-            "* %s",
-            line
-          );
+          writefln("* %s", line);
         }
       }
       if (!line.empty) {
@@ -1310,8 +1306,7 @@ template docAbstraction() {
         }
       }
     }                                                                           /+ ← srcDocLoop closed: loop markup document/text line by line +/
-                                                                                /+ ↓ post loop markup document/text +/
-                                                                                /+ ↓ post loop markup document/text +/
+    /+ ↓ post loop markup document/text +/
     { // EOF
       comp_obj_heading_                                              = comp_obj_heading_.init;
       comp_obj_heading_.metainfo.is_of_part                          = "backmatter";
@@ -4049,7 +4044,7 @@ template docAbstraction() {
       }
       an_object[an_object_key] ~= line ~= "\n";
       an_object["lev"] ~= m.captures[1];
-      assertions_doc_structure(an_object, lv); // includes most of the logic for collapsed levels
+      assertions_doc_structure(an_object, an_object_key, lv); // includes most of the logic for collapsed levels
       switch (an_object["lev"]) {
       case "A":                                // Title set
         if ((an_object[an_object_key].match(rgx.variable_doc_title_author_date))
@@ -6165,173 +6160,568 @@ template docAbstraction() {
                                                                                 /+ ↓ abstraction functions assertions +/
   @safe pure void assertions_doc_structure()(
     string[string]  an_object,
+    string          an_object_key,
     int[string]     lv
   ) {
+    string msg_error_doc_struct = "\nERROR in document structure, check markup (heading level relationships):\n";
     if (lv["h3"] > eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h1"] > eN.bi.off);
-      assert(lv["h2"] > eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h1"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     } else if (lv["h2"] > eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h1"] > eN.bi.off);
-      assert(lv["h3"] == eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h1"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     } else if (lv["h1"] > eN.bi.off) {
-      assert(lv["h0"] > eN.bi.off);
-      assert(lv["h2"] == eN.bi.off);
-      assert(lv["h3"] == eN.bi.off);
+      assert(lv["h0"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     } else if (lv["h0"] > eN.bi.off) {
-      assert(lv["h1"] == eN.bi.off);
-      assert(lv["h2"] == eN.bi.off);
-      assert(lv["h3"] == eN.bi.off);
+      assert(lv["h1"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     } else {
-      assert(lv["h0"] == eN.bi.off);
-      assert(lv["h1"] == eN.bi.off);
-      assert(lv["h2"] == eN.bi.off);
-      assert(lv["h3"] == eN.bi.off);
+      assert(lv["h0"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h1"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     }
     if (lv["h7"] > eN.bi.off) {
-      assert(lv["h4"] > eN.bi.off);
-      assert(lv["h5"] > eN.bi.off);
-      assert(lv["h6"] > eN.bi.off);
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     } else if (lv["h6"] > eN.bi.off) {
-      assert(lv["h4"] > eN.bi.off);
-      assert(lv["h5"] > eN.bi.off);
-      assert(lv["h7"] == eN.bi.off);
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     } else if (lv["h5"] > eN.bi.off) {
-      assert(lv["h4"] > eN.bi.off);
-      assert(lv["h6"] == eN.bi.off);
-      assert(lv["h7"] == eN.bi.off);
+      assert(lv["h4"] > eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     } else if (lv["h4"] > eN.bi.off) {
-      assert(lv["h5"] == eN.bi.off);
-      assert(lv["h6"] == eN.bi.off);
-      assert(lv["h7"] == eN.bi.off);
+      assert(lv["h5"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     } else {
-      assert(lv["h4"] == eN.bi.off);
-      assert(lv["h5"] == eN.bi.off);
-      assert(lv["h6"] == eN.bi.off);
-      assert(lv["h7"] == eN.bi.off);
+      assert(lv["h4"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     }
     if (lv["h0"] == eN.bi.off) {
-      assert(lv["h1"] == eN.bi.off);
-      assert(lv["h2"] == eN.bi.off);
-      assert(lv["h3"] == eN.bi.off);
-      assert(lv["h4"] == eN.bi.off);
-      assert(lv["h5"] == eN.bi.off);
-      assert(lv["h6"] == eN.bi.off);
-      assert(lv["h7"] == eN.bi.off);
+      assert(lv["h1"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h2"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h4"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ "missing segment level 1~\n"
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h5"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     }
     if (lv["h1"] == eN.bi.off) {
-      assert(lv["h2"] == eN.bi.off);
-      assert(lv["h3"] == eN.bi.off);
+      assert(lv["h2"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     }
     if (lv["h2"] == eN.bi.off) {
-      assert(lv["h3"] == eN.bi.off);
+      assert(lv["h3"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     }
     if (lv["h3"] == eN.bi.off) {
     }
     if (lv["h4"] == eN.bi.off) {
-      assert(lv["h5"] == eN.bi.off);
-      assert(lv["h6"] == eN.bi.off);
-      assert(lv["h7"] == eN.bi.off);
+      assert(lv["h5"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h6"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     }
     if (lv["h5"] == eN.bi.off) {
-      assert(lv["h6"] == eN.bi.off);
-      assert(lv["h7"] == eN.bi.off);
+      assert(lv["h6"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     }
     if (lv["h6"] == eN.bi.off) {
-      assert(lv["h7"] == eN.bi.off);
+      assert(lv["h7"] == eN.bi.off,
+        msg_error_doc_struct
+        ~ an_object[an_object_key]
+      );
     }
     if (lv["h7"] == eN.bi.off) {
     }
     switch ((an_object["lev"]).to!string) {
     case "A":
       if (lv["h0"] == eN.bi.off) {
-        assert(lv["h1"] == eN.bi.off);
-        assert(lv["h2"] == eN.bi.off);
-        assert(lv["h3"] == eN.bi.off);
-        assert(lv["h4"] == eN.bi.off);
-        assert(lv["h5"] == eN.bi.off);
-        assert(lv["h6"] == eN.bi.off);
-        assert(lv["h7"] == eN.bi.off);
+        assert(lv["h1"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level A~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h2"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level A~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h3"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level A~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h4"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 1~\n"
+          ~ "at level A~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h5"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level A~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h6"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level A~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h7"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level A~\n"
+          ~ an_object[an_object_key]
+        );
       } else {                       // (lv["h0"] > eN.bi.off)
-        assert(lv["h0"] == eN.bi.off,"error should not enter level A a second time");
+        assert(lv["h0"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "should not enter level A a second time\n"
+          ~ "at level A~\n"
+          ~ an_object[an_object_key]
+        );
       }
       break;
     case "B":
       if (lv["h1"] == eN.bi.off) {
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h2"] == eN.bi.off);
-        assert(lv["h3"] == eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level B~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h2"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level B~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h3"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level B~\n"
+          ~ an_object[an_object_key]
+        );
       } else {                       // (lv["h1"] > eN.bi.off)
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h1"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level B~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h1"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level B~\n"
+          ~ an_object[an_object_key]
+        );
       }
       break;
     case "C":
       if (lv["h2"] == eN.bi.off) {
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h1"] > eN.bi.off);
-        assert(lv["h3"] == eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level C~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h1"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "level C should not follow level A\n"
+          ~ "at level C~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h3"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level C~\n"
+          ~ an_object[an_object_key]
+        );
       } else {                       // (lv["h2"] > eN.bi.off)
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h1"] > eN.bi.off);
-        assert(lv["h2"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level C~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h1"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level C~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h2"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level C~\n"
+          ~ an_object[an_object_key]
+        );
       }
       break;
     case "D":
       if (lv["h3"] == eN.bi.off) {
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h1"] > eN.bi.off);
-        assert(lv["h2"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level D~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h1"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "level D should not follow level A\n"
+          ~ "at level D~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h2"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level D~\n"
+          ~ an_object[an_object_key]
+        );
       } else {                      // (lv["h3"] > eN.bi.off)
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h1"] > eN.bi.off);
-        assert(lv["h2"] > eN.bi.off);
-        assert(lv["h3"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level D~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h1"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level D~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h2"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level D~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h3"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level D~\n"
+          ~ an_object[an_object_key]
+        );
       }
       break;
     case "1":
       if (lv["h4"] == eN.bi.off) {
-        assert(lv["h0"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 1~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h5"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 1~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h6"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 1~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h7"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 1~\n"
+          ~ an_object[an_object_key]
+        );
       } else {                      // (lv["h4"] > eN.bi.off)
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h4"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 1~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h4"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 1~ ?\n"
+          ~ "at level 1~\n"
+          ~ an_object[an_object_key]
+        );
       }
       break;
     case "2":
       if (lv["h5"] == eN.bi.off) {
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h4"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 2~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h4"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 1~ ?\n"
+          ~ "at level 2~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h6"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 2~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h7"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 2~\n"
+          ~ an_object[an_object_key]
+        );
       } else {                      // (lv["h5"] > eN.bi.off)
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h4"] > eN.bi.off);
-        assert(lv["h5"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 2~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h4"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 1~ ?\n"
+          ~ "at level 2~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h5"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 2~\n"
+          ~ an_object[an_object_key]
+        );
       }
       break;
     case "3":
       if (lv["h6"] == eN.bi.off) {
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h4"] > eN.bi.off);
-        assert(lv["h5"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 3~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h4"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 1~ ?\n"
+          ~ "at level 3~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h5"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 2~ ?\n"
+          ~ "at level 3~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h7"] == eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 3~\n"
+          ~ an_object[an_object_key]
+        );
       } else {                      // (lv["h6"] > eN.bi.off)
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h4"] > eN.bi.off);
-        assert(lv["h5"] > eN.bi.off);
-        assert(lv["h6"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 3~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h4"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 1~ ?\n"
+          ~ "at level 3~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h5"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 3~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h6"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 3~\n"
+          ~ an_object[an_object_key]
+        );
       }
       break;
     case "4":
       if (lv["h7"] == eN.bi.off) {
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h4"] > eN.bi.off);
-        assert(lv["h5"] > eN.bi.off);
-        assert(lv["h6"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 4~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h4"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 1~ ?\n"
+          ~ "at level 4~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h5"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 2~ ?\n"
+          ~ "at level 4~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h6"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 3~ ?\n"
+          ~ "at level 4~\n"
+          ~ an_object[an_object_key]
+        );
       } else {                      // (lv["h7"] > eN.bi.off)
-        assert(lv["h0"] > eN.bi.off);
-        assert(lv["h4"] > eN.bi.off);
-        assert(lv["h5"] > eN.bi.off);
-        assert(lv["h6"] > eN.bi.off);
-        assert(lv["h7"] > eN.bi.off);
+        assert(lv["h0"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 4~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h4"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "missing segment level 1~ ?\n"
+          ~ "at level 4~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h5"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 4~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h6"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 4~\n"
+          ~ an_object[an_object_key]
+        );
+        assert(lv["h7"] > eN.bi.off,
+          msg_error_doc_struct
+          ~ "at level 4~\n"
+          ~ an_object[an_object_key]
+        );
       }
       break;
     default: