... and (drum roll) with a slight patch to detect "shall", "may", "should" also inside footnotes, we now find

lex.tex:672:characters may produce a long external identifier, but \Cpp{} does not <--- "shall", "should", or "may" inside a note
preprocessor.tex:558:a preprocessing token shall not follow a <--- "shall", "should", or "may" inside a note
preprocessor.tex:564:comments may appear anywhere in a source file, <--- "shall", "should", or "may" inside a note
support.tex:2490:expression, may, however, increase the \tcode{size} argument to <--- "shall", "should", or "may" inside a note
templates.tex:9077:may be deduced from an array bound, the resulting value will always be <--- "shall", "should", or "may" inside a note

@godbyk , I think I need your help here. Please have a look at this pull request and consider the definition of the "footnoteenv" macro in macros.tex. The goal is to have a proper environment for footnotes and not the inline-style \footnote{...} stuff. The proper environment helps our script-based sanity checking of the LaTeX source code.

I essentially got it working with some "lrbox" operations, and it looks as before (except for a hyphenation change that I can only explain by some difference in hyphenation regime in footnotes, but that's not the point here).

In order to make the "footnoteenv" work inside tables inside floats, I need to make sure I employ \global to have the footnote's contents "escape" properly. So far, so good. However, I am unable to achieve this with a named box; it only works with a numbered box. See the line that copies the local \box99 to the \global named box. Of course, using a specific numbered box risks conflicts. For example, \box0 seems to cause such a conflict; all page numbers in the cross-reference are off by the size of the table of contents. My attempts at using a named box have failed with "expected a <box> here" errors. Do you have any ideas?

Rebased due to conflict.

Rebased again. This is now ready for revuew/merge, from my perspective.
Two diff's remain: One hyphenation change (for unknown reasons), one removed space before the footnote number in the running text (a clear improvement)