Changing text appearance in Emacs: overlays work, text properties don't

Question

I've been experimenting today with text properties in Emacs. If I position the cursor on a line with some text on it and then execute the following code with M-:, the line is redisplayed in bold.

(overlay-put
 (make-overlay
  (line-beginning-position)
  (line-end-position))
 'face 'bold)

If, however, I wipe out the overlay with (remove-overlays) and execute the following code, nothing happens (except that the word "nil" appears in the minibuffer).

(put-text-property
 (line-beginning-position)
 (line-end-position)
 'face 'bold)

From what I've gleaned so far, I'd expect that these two snippets should produce the same visual results. Why don't they?

Cusack

Works for me with Emacs 23.1, with text in a buffer in both fundamental-mode and text-mode. – Overweary

22.1.50 isn't an official build, I'd try grabbing an official release from homepage.mac.com/zenitani/emacs-e.html – Overweary

I downloaded and installed the official release, and the same problem occurred. But I chanced upon the answer regardless. I opened a new empty buffer and typed some random gibberish, and setting text properties worked there. The buffer I tried all my experiments in originally was in xml-mode (or sgml-mode, whatever). So at least I can apply text properties now, but it's still a mystery to me how (and why) certain modes can countermand put-text-property. – Cusack

Answer 1

When font-lock-mode is on, the face attribute will be overridden. Try font-lock-face instead:

(put-text-property
 (line-beginning-position)
 (line-end-position)
 'font-lock-face 'bold)

Paste

Answer 2

ansi-color.el -- "In Emacs, however, things are a bit different: When font-lock is active in a buffer, you cannot simply add face text-properties to the buffer. Font-lock will remove the face text-property using 'font-lock-unfontify-region-function'. If you want to insert the strings returned by 'ansi-color-apply' into such buffers, you must set 'font-lock-unfontify-region-function' to `ansi-color-unfontify-region'. This function will not remove all face text-properties unconditionally. It will keep the face text-properties if the property 'ansi-color' is set.

Eternal