Re: whitespace includes U+3000

[Richard Stallman]

    >     No.  The current Emacs treat only TAB and SPACE as
    >     "whitespace" characters.

    > It would be very easy to fix this by setting the syntax table entries
    > for those characters--if there are not too many of them.  So why not
    > fix it?

    Are you sure that "whitespace" of syntax has the same
    meaning as the "whitespace" of show-trailing-whitespace?

I am not sure which one we're talking about here.
Is it show-trailing-whitespace?

If so, that would also be easy to change, if it ought to be changed.

    For instance, currently ^L (formfeed) has syntax
    "whitespace".  But, it is displayed with glyph "^L".  Should
    it be the target of show-trailing-whitespace?

No.

    For instance, currently NBSP (U+00A0) has syntax "."
    (punctuation), and it is displayed with special face to
    indicated the existing of that character.  Should it be
    changed to "whitespace" syntax, or shoudn't be changed?

The special face for that character should not be overridden, but the
other whitespace after it _and before it_ should probably be displayed
specially by show-trailing-whitespace.

You can probably get this result by putting NBSP into the pattern
for show-trailing-whitespace to recognize.  Redisplay will override
the face, for the NBSP.