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I know by M-x set-background-color or M-x set-foreground-color one can change the background/foreground of the the entire buffer. Of course this color change only persists in the current session.

In the same way how can one change the background/foreground color of some characters/words?

For example if in a buffer I have something like below

enter image description here

I would like to change the background/foreground color of some characters like below:

enter image description here

And I would like that this color change to be persistent in the current session unless I delete these colorful character.

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It's not very clear what you are asking, IMO.

There are various ways to highlight a particular character (e.g. everywhere in the region or in a buffer). Library highlight-chars.el provides one approach.

Likewise, there are various ways to highlight a word (e.g. everywhere in the region or in a buffer). Library Highlight provides one approach. Ordinary font-lock and hi-lock provides another.

Are you also asking about persistence of such highlighting past the current session? If so, that too is possible.

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10
  • I added some explanations. – Name Aug 5 '15 at 19:58
  • I tested highlight-chars.el, it highlights all occurrences of a character. Thus this does not provide the feature I have asked, but it is very useful. Thank you for introducing it. – Name Aug 5 '15 at 20:12
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    I have tested your second link emacswiki.org/emacs/HighlightLibrary. By M-x hlt-highlight-region I can highlight a region (this region can be a character, a word, etc). The background color is fixed (green). For background color, this partially answer the question. But for foreground color the question still remains. Also if I would like to use different colors, the question still remains. – Name Aug 5 '15 at 20:23
  • Read the commentary of the library and the doc strings of the things you use. See, for example, command hlt-choose-default-face, mentioned in the doc string of command hlt-highlight-region. And read about Emacs faces in the Emacs manual. – Drew Aug 6 '15 at 0:29
  • It turns out that the package highlight is exactly what I was looking for. I am trying to use it and to be familiar with it. By hlt-choose-default-face one can actually use different colors for highlighting (like the second image in my original post). – Name Aug 6 '15 at 11:07
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This demonstration defines a highlighting color and commands which use anonymous faces to highlight a character or word.

(defvar my-hl-color "#ff00ff")

(defun my-hl-thing (boundaries)
  (put-text-property (car boundaries) (cdr boundaries)
                     'font-lock-face `(:background ,my-hl-color)))

(defun my-hl-character ()
  (interactive)
  (my-hl-thing (cons (point) (1+ (point)))))

(defun my-hl-word ()
  (interactive)
  (my-hl-thing (bounds-of-thing-at-point 'word)))
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  • Thank you. my-hl-character seems to work, but let me report that when the character is in a comment area it seems to not working. Let me also report that when a word is the last word of buffer it seems that my-hl-word seems to not properly work. – Name Aug 5 '15 at 21:33

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