The symbol + can be problematic when it occurs in inline text. While there are other ways to escape it, it seems to be a good candidate as an intrinsic attribute for the same reason several of the others (e.g., two-colons, two-semicolons, etc) where selected.

This issue is a feature request to add the following attribute definition to asciidoc.conf

[attributes] plus=+

This can be used inline as {plus}.

...which would render:

This can be used inline as +.

plus=+ won't work due to the substitution order, I've added plus=+ See https://code.google.com/p/asciidoc/source/detail?r=52072cf4b75d016ea9e30c56ef21dd747663c913

Ah, of course! (I was just studying substitution rules today, in fact). Nice solution. Thanks!