regexp with negative lookbehind leads to empty list of lexemes in Safari

[Ansa211]

The Safari Web browser (I am told this is the primary choice for Mac users) does not understand regexes with negative look behind. We have at least one in our code (lexeme.js, line 1), which leads to the bug described below.

These StackOverflow answers may be useful:
https://stackoverflow.com/questions/67332407/how-to-not-match-given-prefix-in-regex-without-negative-lookbehind
https://stackoverflow.com/questions/641407/javascript-negative-lookbehind-equivalent

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Thanks to @stranak for reporting this issue:

V Safari na macu se nenačte datový soubor, appka je prázdná. Přikládám, co mi browser k tomu řekl.

[Ansa211]

The particular regex causing the issue observed by @stranak was introduced in 9fcfb5f, so it only applies to version 4.0 of the website and not to the earlier versions.