postcss-px-to-viewport/src/pixel-unit-regexp.js

// excluding regex trick: http://www.rexegg.com/regex-best-trick.html

// Not anything inside double quotes
// Not anything inside single quotes
// Not anything inside url()
// Any digit followed by px
// !singlequotes|!doublequotes|!url()|pixelunit
function getUnitRegexp(unit) {
  return new RegExp('"[^"]+"|\'[^\']+\'|url\\([^\\)]+\\)|(\\d*\\.?\\d+)' + unit, 'g');
}

module.exports = {
  getUnitRegexp
};