show cssText
parse cssText
handle errors locally when parsing CSS text
move css models next to other model classes
createPropertyModels method
create property models from css text
implement replaceRule using insertRule/deleteRule
redo updatePropertyValue to check for successful update
show error message on failed property value update
manage property parsing errors
use "; " to split CSS text when parsing
Show error message for errors other than InvalidPropertyValueError
Help for error messages
click on property to clear unsaved changes & errors