Find a node in a tag table.
MARKER specifies the buffer and position to start searching at.
REGEXP is a regular expression matching nodes or references. Its first
group should match `Node:' or `Ref:'.
If a match was found, value is a list (FOUND-ANCHOR POS MODE), where
FOUND-ANCHOR is non-nil if a `Ref:' was matched, POS is the position
where the match was found, and MODE is `major-mode' of the buffer in
which the match was found.
This function tries to find a case-sensitive match first, then a
case-insensitive match is tried.