+(defconst elpher-url-regex
+ "\\([a-zA-Z]+\\)://\\([a-zA-Z0-9.-]*[a-zA-Z0-9-]\\|\\[[a-zA-Z0-9:]+\\]\\)\\(:[0-9]+\\)?\\(/\\([0-9a-zA-Z_~?/@|:.%#=&-]*[0-9a-zA-Z_~?/@|#-]\\)?\\)?"
+ "Regexp used to locate and buttonify URLs in text files loaded by elpher.")
+
+(defun elpher-buttonify-urls (string)
+ "Turn substrings which look like urls in STRING into clickable buttons."
+ (with-temp-buffer
+ (insert string)
+ (goto-char (point-min))
+ (while (re-search-forward elpher-url-regex nil t)
+ (let ((page (elpher-page-from-url (substring-no-properties (match-string 0)))))
+ (make-text-button (match-beginning 0)
+ (match-end 0)
+ 'elpher-page page
+ 'action #'elpher-click-link
+ 'follow-link t
+ 'help-echo #'elpher--page-button-help
+ 'face 'button)))
+ (buffer-string)))
+
+
+;; ANSI colors or XTerm colors (application and filtering)
+
+(or (require 'xterm-color nil t)
+ (require 'ansi-color))
+
+(defalias 'elpher-color-filter-apply
+ (if (fboundp 'xterm-color-filter)
+ (lambda (s)
+ (let ((_xterm-color-render nil))
+ (xterm-color-filter s)))
+ #'ansi-color-filter-apply)
+ "A function to filter out ANSI escape sequences.")
+
+(defalias 'elpher-color-apply
+ (if (fboundp 'xterm-color-filter)
+ #'xterm-color-filter
+ #'ansi-color-apply)
+ "A function to apply ANSI escape sequences.")
+
+(defun elpher-text-has-ansi-escapes-p (string)
+ "Return non-nil if STRING includes an ANSI escape code."
+ (save-match-data
+ (string-match "\x1b\\[" string)))
+
+
+;; Processing text for display
+
+(defun elpher-process-text-for-display (string)
+ "Perform any desired processing of STRING prior to display as text.
+Currently includes buttonifying URLs and processing ANSI escape codes."
+ (elpher-buttonify-urls (if (elpher-text-has-ansi-escapes-p string)
+ (if elpher-filter-ansi-from-text
+ (elpher-color-filter-apply string)
+ (elpher-color-apply string))
+ string)))
+
+
+;;; General network communication