Why this regular is not recognized?

[ccl20210529]

(?<=\d{6})\d{10}(?=.{2})

[wzhck]

(?<=\d{6}) is a lookbehind ((?<=) or (?<!)), which is NOT supported by JavaScript. In fact JavaScript can support your lookahead(?=.{2})((?=) or (?!)).

You can use (?=\d{6})\d{10}(?=.{2}) instead (ref: javascript-regex-look-behind-alternative):

[alexetgus]

The Javascript used is very minimalist. It does not dwell on the particularities of PCRE Regex...

[liudongmiao]

demo: https://jianyu.io/regulex/