🚀 go-pugleaf

Shinichirou Sugou writes:
 > I think there is a bug in 're-search-backward' function.
 > [...]
 > [Reproduction]
 > (1) Open a empty buffer (says foo); type two characters, SPACE and 'a'; move
 >     the cursor just on the character 'a'.
 > (2) Eval (re-search-backward "\\`\\|\\s ")
 > (3) Eval (match-data)
 >     and you will see (#<marker at 1 in foo> #<marker at 1 in foo> )
 > 
 > [Bug]
 > In 're-search-backward', not "\\`" but "\\s " should be matched.  But
 > 'match-data' says that actual matching is "\\'".

You seem to be assuming that the alternative operator will always match
the largest of the two alternatives.  The documentation for `\|' does
not guarantee this.   From the _GNU Emacs Manual_, Section 13.5, "Syntax
of Regular Expressions"

     `\|' applies to the largest possible surrounding expressions.  Only
     a surrounding `\( ... \)' grouping can limit the grouping power of
     `\|'.

This statement applies to the regular expression itself, not the text
that is being matched.