Updated documentation to remove mention of HTML::Selector and clarify what is expected of a selector now.
Fixed a Nokogiri::CSS::SyntaxError by using its expected format for unicode characters.
Updated testing guide to reflect changes in ActionDispatch::SelectorAssertions.
Removed test method that used assert_tag.
Fixed typo in method name. Fixed Nokogiri::CSS::SyntaxError.
Reverted some changes in the guide.
Readded some documentation about substitution values.
Added implementation for substitution values via Nokogiri's custom pseudo classes.
Fixed nested assert_select bug. Trying to create a full document for a nested call that already had a document.