As you type, the editor performs syntax checking on the script in the background. When we have errors in the script, it shows the error in the margins and the text will get a red squiggle under it to mark where the JavaScript interpreter found an error.
When you mouse over the error mark in the ruler (the left margin) we see the error message in a popup window.
The ruler on the left is synchronized with the text window, and a mark is directly related to the line in the text window. If there are no errors in the text we see in the window, there will be no marks in this ruler either.
However, the overview ruler on the right shows all errors in the entire script regardless of where the text editor is positioned. When you mouse over the mark in the ruler you get the same error message popup as you get in the left ruler. Clicking on the marker repositions the editor to the line where the problem was identified.
Parent topic: JavaScript Enhancements