ErrorDisplayEnabled slower than event ?

Yes there is a delay in there by design. You have to consider that most of the time, people will be typing in an editor and during that time, the state of the code will be invalid. People don't want to see error lines show up right after they press a key since they may not be finished typing the code line yet. Therefore, we introduce a small delay before showing errors. This allows errors to show up during typing pauses but not be showing up constantly in the middle of typing, leading to a better user experience. This is what products like Visual Studio do as well.

Then delay can be controlled by SyntaxLanguage.UserInterfaceUpdateDelay.

Thank you !