If there is no full match for the pattern, or there
are several matches, the "best" match will be used.
A sophisticated algorithm is used to decide which
match is better than another one.  These items are
considered in the computation:
    - A match with same case is much better than a match
      with different case.
    - A match that starts after a non-alphanumeric
      character is better than a match in the middle of a
      word.
    - A match at or near the beginning of the tag is
      better than a match further on.
    - The more alphanumeric characters match, the better.
    - The shorter the length of the match, the better.

:set helpfile?
helpfile=/usr/share/nvim/runtime/doc/help.txt
:echo $VIMRUNTIME
/usr/share/nvim/runtime
:echo $VIM
/usr/share/nvim