Here is what sys/news3400/README had to say:
# could get the changed value notification long after the value
。关于这个话题，WPS官方版本下载提供了深入分析
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this isn’t just an academic curiosity. flip the alternation order to (ab|a)+ and suddenly PCRE matches the entire string! the | operator in backtracking engines is ordered - it’s not union, it’s “try left first”. the order of branches changes the result, which means | is not commutative. a|b and b|a can give different matches.