I want to add extra expressions to some JS code, but taking care of the correct element ID (in the example below, the ID is scatter).

document.getElementById("scatter").height="400"; -->
document.getElementById("scatter").height="400"; document.getElementById("scatter").style="visibility: visible"; 

My attempt so far has been:

M-x replace-regexp RET 
Id("\(\w+\)").height="400"; RET 
Id("\0").height="400"; document.getElementById("\0").style="visibility: visible";

Where \(\w+\) grabs the element ID and \0 references it on the replacement string. Unfortunately replace-regexp is complaining that I'm using \incorrectly.

Could anyone point out what I'm doing wrong?

  • 1
    Try \1 instead of \0.
    – Drew
    Jul 2, 2016 at 14:23
  • That solved it, thx.
    – Daniel
    Jul 2, 2016 at 14:25

1 Answer 1


In a regexp replacement pattern, \N matches a subgroup, and \1, not \0 matches the first subgroup.

I just filed Emacs bug #23884 to help clarify the doc about this.

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