When creating value-matching CSS expressions in C#, it's quite convenient to replace double quotes with single quotes (which is also valid in XML for attributes, FWIW). This avoids having to escape the quotes, when the matched values contain spaces.

In addition to the implicit quotes we already do (i.e. span[text()*=hello world] works just fine), doing normalization on single quotes too would be convenient, since it would Just Work regardless of the quote format you used (or not).