Hi Juriy,

The regexp backreferences usage in ignoreCustomFragments was affected from 3.0.3 version, here my case:

{
  ignoreCustomFragments: [ /<(WC@[\s\S]*?)>(.*?)<\/\1>/ ]
}

The grouping update of regexp expression in the code below (htmlminifier.js) was the problem because the \1 backreference points to first group and not to ignoreCustomFragments group expression (so logically my regexp stop working):

in v3.0.3:

new RegExp('\s_(?:' + customFragments.join('|') + ')+\s_', 'g')

in v3.1.0:

new RegExp('(\s_)(?:' + customFragments.join('|') + ')+(\s_)', 'g');

any plans of update ?
Thks !!!