+(defun ispell--\\w-filter (char)
+ "Return CHAR in a string when CHAR doesn't have \"word\" syntax,
+nil otherwise. CHAR must be a character."
+ (let ((str (string char)))
+ (and
+ (not (string-match "\\w" str))
+ str)))
+
+(defun ispell--make-\\w-expression (chars)
+ "Make a regular expression like \"\\(\\w\\|[-_]\\)\".
+This (parenthesized) expression matches either a character of
+\"word\" syntax or one in CHARS.
+
+CHARS is a string of characters. A member of CHARS is omitted
+from the expression if it already has word syntax. (Be careful
+about special characters such as ?\\, ?^, ?], and ?- in CHARS.)
+If after this filtering there are no chars left, or only one, a
+special form of the expression is generated."
+ (let ((filtered
+ (mapconcat #'ispell--\\w-filter chars "")))
+ (concat
+ "\\(\\w"
+ (cond
+ ((equal filtered "")
+ "\\)")
+ ((eq (length filtered) 1)
+ (concat "\\|" filtered "\\)"))
+ (t
+ (concat "\\|[" filtered "]\\)"))))))
+
+(defun ispell--make-filename-or-URL-re ()
+ "Construct a regexp to match some file names or URLs or email addresses.
+The expression is crafted to match as great a variety of these
+objects as practicable, without too many false matches happening."
+ (concat ;"\\(--+\\|_+\\|"
+ "\\(/\\w\\|\\("
+ (ispell--make-\\w-expression "-_")
+ "+[.:@]\\)\\)"
+ (ispell--make-\\w-expression "-_")
+ "*\\([.:/@]+"
+ (ispell--make-\\w-expression "-_~=?&")
+ "+\\)+"
+ ;"\\)"
+ ))
+