* .ssm can contain/include .sst or .ssi
.sst files can be processed independently, they do not contain other files
.ssi files have been only insertions of text & are not processed independently
but as part of an ssm
change proposed:
.ssm unchanged,
.sst unchanged,
.ssi as before, but can include .sst or .ssi, so:
files are only insertions & are not processed independently but as part of an
.ssm or another .ssi
i.e. as before with the addition that it like a .ssm can contain/include
.sst or .ssi
* requested feature, (Closes: #744408)
User beware. In previous versions there has been a deliberate attempt to keep
it easy to follow documents & not have to dig through different levels of
includes, as this is more likely to lead to errors in markup.
The idea of nested includes has not been attractive (messy for a document),
however, this is now made possible, use with care
* it is not as easy to see document structure at a glance, and structural
errors may be introduced and will need to be taken care of (requiring
document markup debugging)
* allowing .ssi to also include other .ssi or .sst could lead to infinite
recursion if an .ssi includes another which includes itself; stopping after
an additional level of includes seems arbitrary, and possibly prone to error
if you are dealing with many documents
* requires testing
* version bump, new behavior added to .ssi one of the 3 sisu filetypes