Re: [dom] matches, querySelector, etc. shouldn't throw on an unrecognized selector (#39)

Though admittedly this isn't an exhaustive search, I'm having a hard time finding a popular JS library that relies on selectors throwing an error to implement their custom functionality.

For instance, [jQuery](https://github.com/jquery/sizzle/blob/a7020477b0433ac08d66baf9eebb3f9d24868e21/src/sizzle.js#L877-L890) and [MooTools](https://github.com/mootools/slick/blob/f9503a24e69e442fa926e34ff85d1cdb874b97bd/Source/Slick.Finder.js#L580-L587) both `return` from within the `try` if `matches` returns a value and try their own implementation if it doesn't.  (The `catch` block is empty.)  Moreover, jQuery's the only one I found in my quick search that implements non-DOM selectors.

As with any proposed change, there is a compatibility risk to assess, but at first blush, I don't see any so large that this isn't worth discussing.

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