xml: markup language attributes take a bcp 47 tag

Spine names a language as the directory under media/text/ is
named, which for a region is the posix form with an underscore,
pt_BR. A lang, xml:lang or dc:language value is a BCP 47 (RFC
3066) tag and wants a hyphen, pt-BR. Spine put its own code
there unchanged, so a document in a region language produced an
invalid attribute in every one of its xhtml files: 138 epubcheck
errors for a document of ten segments and a navigation file.

src.language_tag is the same language as a tag. The attributes
and the dc metadata now read it. Output paths keep src.language,
since a path is named after the directory, not after the tag.

(assisted by Claude-Code)

1 files changed, 15 insertions, 0 deletions

diff --git a/src/sisudoc/ocda/io_in/paths_source.d b/src/sisudoc/ocda/io_in/paths_source.d
index 9cacdf0..f32b89e 100644
--- a/src/sisudoc/ocda/io_in/paths_source.d
+++ b/src/sisudoc/ocda/io_in/paths_source.d
@@ -298,6 +298,21 @@ template PathMatters() {
           string language() {
             return lng();
           }
+          /+ ↓ the same language, as a language tag rather than as spine's
+               own code. Spine names a language the way a directory under
+               media/text/ is named, which for a region is the posix form
+               with an underscore, pt_BR. A lang, xml:lang or dc:language
+               value is a BCP 47 (RFC 3066) tag and wants a hyphen, pt-BR;
+               an underscore there is invalid and every xhtml file in the
+               document carrying it is an epubcheck error. Every other code
+               spine knows (from the document sample set) is two letters,
+               where the two forms are equal, which is why only a region
+               code shows this up.
+          +/
+          string language_tag() {
+            import std.array : replace;
+            return lng().replace("_", "-");
+          }
           string file_with_absolute_path() {
             return _env["pwd"].chainPath(path_and_fn).array;
           }