Combining of CSS rules breaks when using browser prefixes and selectors

[BradMclain]

For example the following:

.search [type="search"]::-webkit-input-placeholder {
  color: rgba(255, 255, 255, 0.4);
}
.search [type="search"]::-moz-placeholder {
  color: rgba(255, 255, 255, 0.4);
}
.search [type="search"]:-ms-input-placeholder {
  color: rgba(255, 255, 255, 0.4);
}
.search [type="search"]::placeholder {
  color: rgba(255, 255, 255, 0.4);
}

Will be rewritten as:

.search [type="search"]::-webkit-input-placeholder,.search [type="search"]::-moz-placeholder,.search [type="search"]:-ms-input-placeholder,.search [type="search"]::placeholder{
  color:rgba(255,255,255,0.4)
}

However standard browser behaviour is to ignore a rule if any selector in a group of selectors is not recognised or is invalid. In this case the browser prefixes will always fail in other browsers so this rule is never applied.

See https://www.w3.org/TR/css3-selectors/#Conformance which has the line:

a group of selectors containing an invalid selector is invalid.

[BradMclain]

Possibly a dupe of #97?