Indentation conventions for Info manuals; recognizing code

[Drew Adams <drew.adams@oracle.com>]

I don't know what conventions/styles are defined for our Info manuals, if there are any.  Is that documented somewhere?

Given only an Info buffer, i.e., not Texinfo source code but its output that's used by Emacs users, is there a convention wrt indentation of, say code blocks?  Or is there some other way (e.g. a text property) to recognize code or similar text that really deserves a fixed-pitch font?

Code blocks, ASCII diagrams, and the like seem to be indented 10 chars in the Elisp manual.

That's a start.  Based on that, I added an experimental option to Info+ to fontify text that's indented at least 10 chars (by default).  The face used is fixed-pitch by default.

(There's also a minor mode that lets you use variable-pitch for the main text body - but that's independent.  Being able to fontify code blocks is useful even when all of the text is fixed-pitch.)

For the Elisp manual this fontifying of indented text (>= 10 chars) works quite well. 

My code also optionally highlights quoted sexps (`...', "...") with fixed-pitch faces (by default), so code is fixed-pitch pretty much everywhere in the Elisp manual, even if you choose to make the main text variable-pitch.  Likewise, ASCII-art diagrams (they seem to be indented 10 chars also).

But other manuals don't seem to use the same indentation.  Several (org, eintr, ccmode, efaq(-w32),...) indent code (including Elisp) 5 spaces - which is the same amount that other, non-code text is indented.

(There are also lines in the Emacs manual and ccmode represent user input or program output.  Those too are indented only 5 chars, so they won't appear in fixed-pitch font.)

And if a code block is indented only 5 chars, but some of its lines are indented at least 10 chars, then this optional fontifying kicks in for those latter lines - not great, obviously.

The CC-Mode manual is somewhat like the Elisp manual - it too indents many code blocks 10 chars, but others are indented 5 chars.

Ccmode also has some bullets that are, themselves, indented under indented paragraphs.  (Why is the bullet itself indented wrt the preceding paragraph?  Same thing for numbered lists - why indent the number itself?)

And the continuation lines of such bullets start at ... 10 chars, so they get fontified (incorrectly).  Some bullets are even indented relative to indented paragraphs, in which case even the bullet line gets fontified (incorrectly).  E.g. (ccmode) `Indentation Commands':

‘<TAB>’ (‘c-indent-command’)
     This command indents the current line.  That is all you need to
     know about it for normal use...
...
      -- User Option: c-tab-always-indent
          This variable modifies how <TAB> operates.
             • When it is ‘t’ (the default), <TAB> simply indents the
               current line.
             • When it is ‘nil’, <TAB> (re)indents the line only if
               point is to the left of the first non-whitespace...

(5 levels of indentation.)

Maybe such a `User Option:' entry could/should really be at the left margin (1-char indent)?  (That would also enable the highlighting I do for `User Option:' lines.)  But this seems to be intentional - it's done in several places.

Ccmode also has subheadings of a sort, with the text that follows being indented 5 chars.  And there can be nested text that's indented still further.

Using “Hungry Delete Mode” with ‘<DEL>’ and ‘C-d’
     Here you toggle Hungry Delete minor mode with ‘M-x
     c-toggle-hungry-state’(1) (*note Minor Modes::.)  This makes
     ‘<DEL>’ and ‘C-d’ do backwards and forward hungry deletion.

     ‘<DEL>’ (‘c-electric-backspace’)
          This command is run by default when you hit the ‘<DEL>’ key.
          When hungry delete mode is enabled, it deletes any amount of

That last text is indented ... 10 chars.  Similarly, these indented subheadings:

     The display of the guessed style contains these elements:

     Placeholder Name
          You should replace this with a style name of your own.
     Parent Style
          The style current when the guessing began, from which the
          guessed style inherits (*note Config Basics::) the settings
          which weren’t guessed.
___

So given only an Info buffer, I know of no good way to distinguish code blocks and such meaningfully.  Is there an indentation style/convention that has some kind of semantics in this regard?  I'm guessing no.

My code that does this works only in an Info buffer - it can't see any Texinfo source.  It just tweaks `Info-fontify-node' to optionally fontify some things.  So like the rest of `Info-fontify-node', it can only distinguish what's distinct in the Info buffer.  If displayed code isn't declared/recognized as such at the buffer level then we're out of luck I guess.

I know that the use of Texinfo output (what ends up as Info buffer text) is wider than just Emacs Info.  But is there, at the Texinfo level at least, some semantic markup that distinguishes something like code?  If there is, could that info be maintained - transferred to Info buffers in some way, or does the translation just have to be lossy in this way?

It would be handy to be able to somehow distinguish lines of code from other indented text.
___

To see what I mean, take a look at the Elisp manual, after loading info+.el.  If you want to also see the main text with variable-pitch, then first turn on minor mode `Info-variable-pitch-text-mode'.  (The fixed-pitch face used by default is ugly, unless you happen to have font Lucida Console.  But you can of course customize it.)  Then, to see the problems mentioned, try a manual such as Ccmode or Org.

https://www.emacswiki.org/emacs/download/info%2b.el