Reduce the scope of the regex

[bmds]

Currently the regex match too broadly especially for the float and clear properties. They allow authors to use block-start and block-end while the specification only defines inline-start and inline-end.

They should be changed so that only code written to the spec will be correctly converted.

[jonathantneal]

Alternatively, this is the use case for PostCSS Value Parser.

[bmds]

Thanks @jonathantneal i'll take a look