bug#28403: 25.2; find-tag works, but xref-find-definitions

[Winston]

Eli asked:
> I guess we can now close the bug report?

>From my standpoint, yes.

However, since xref-find-definitions is not a drop-in replacement for
find-tag (differences incl. find partial name differs, goes to the
string at (point) without prompting, etc.), I probably won't be the last
person running into the differences.

Perhaps the simplest solution is to expand the documentation section of
xref-find-definitions with text such as the following (corrected for
anything I've got wrong below).  :-)

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xref-find-definitions differs from find-tag several ways:
* find-tag always prompted for a name, with the string at (point) as
  the default name.  With no argument, xref-find-definitions does not
  prompt, and tries immediately to go to a tag with that default name.
  Use (setq xref-prompt-for-identifier t) to force prompting. 
* find-tag allowed partial names.  xref-find-definitions does not.
  Use TAB after a partial name in a prompt for completion(s).
* If find-tag finds your tags OK but xref-find-definitions does not, you
  may need to use --regexp with etags to help it identify the tag name.
  (See etags man page.)  If even that doesn't help, try
                                                        {whatever Dmitry
  and Eli decide is a good long-term easy way to add '(tag-symbol-match-p)
  to etags-xref-find-definitions-tag-order}.

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Thanks for your help!  HTH,
 -WBE