Support complex nested caps arguments with equals in them.
Support complex nested caps arguments with equals in them.

web-animations/web-animations-js-legacy,beni55/web-animations-js-legacy,web-animations/web-animations-js-legacy,web-animations/web-animations-js-legacy,beni55/web-animations-js-legacy,beni55/web-animations-js-legacy,beni55/web-animations-js-legacy