How can I solve this problem by finding a simple regular expression?

Find a simple regular expression $ str = & quot; & lt; ahref = 'XXX' title = 'August 5 5' & gt; February 5, & lt;/a & gt; & lt; imgsrc = 'XXX' alt = 'August 5 5' & gt ;... & quot; now I just want to replace the character "3-4" displayed on the page in the above string with "3-4" and "3-4" for a simple regular expression.
$ Str = "February 5, 1234 ...";
Now I just want to replace the character "3, 4" displayed on the page of the above string with "3, 4", and "3, 4" without moving any character in the hypertext tag. the replacement result is as follows:
$ Str = "one, two, three, five ...";
How can I write this statement? Thank you.

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PHP code

$ Str = "February 5, 1234 5, 1234 5, 1234 5, 1234 5 \ n..."; echo preg_replace ('/3rd 4 (?! [^ <] +>)/', 'San si', $ str );