Insert closing delimiter char(s), i.e. parenthesis, bracket(s), brace(s) or whatever is needed - think of syntactic consequence.
Honor multi-char pairs like triplequoted string, padding and escape-sequences.
For example when called at the end of an open string like
"\(^ *\|^Foo: *\|\( BAR\|'s\|Bad\|BAZ\|Bnter\(?: \(?:\(?:sam\|th
C-u M-x syntactic-close RET should result in
"\(^ *\|^Foo: *\|\( BAR\|'s\|Bad\|BAZ\|Bnter\(?: \(?:\(?:sam\|th\)\)\)\)\)"
That way continuation may be inserted by just one key.
Sometimes language-specific treatment is needed.
Currently supports the following modes:
agda2-mode emacs-lisp-mode html-mode js-mode mhtml-mode nxml-mode org-mode php-mode python-mode ruby-mode sgml-mode web-mode xml-mode xxml-mode
Feel free to file a feature request should your favourite mode not being mentioned.
A first draft was proposed at emacs-devel mailing-list: http://lists.gnu.org/archive/html/emacs-devel/2013-09/msg00512.html