Can't combine selectors using commas in CSS

Question

HTML5 placeholders always appear slightly higher than the center of the input, so I'm trying to use CSS like ::-webkit-input-placeholder to push them down a bit. For some reason, I can't combine the selectors. Here's a Fiddle demonstrating this: http://jsfiddle.net/n7VV7/

I don't want to separate them because I use a CSS compression tool that automatically combines lines. Right now, I can manually separate them, but in the future, I will forget that I can't combine these lines.

Answer 1

You can't use commas to combine vendor-prefixed selectors because when a browser encounters a selector it does not understand, that line is "thrown out." This is why it's necessary to break up vendor prefixes for any selector, not just the :: pseudo-classes.

Here's a link to a CSS-Tricks comment on the problem.

Answer 2

It seems that it is impossible to combine them in one selector, because input-placeholder selectors are used only separately and it is described in a standard.

There is a similar question around: Why isn't it possible to combine vendor-specific pseudo-elements/classes into one rule set?