Available for all ScriptLines.
At the bottom of the Properties Inspector, there is a memo field labeled "Comments". It allows you to insert comments about the currently selected ScriptLine. These can be a "to do" list, or explanations for some of the settings used so that you, or another user, can understand what you did when it comes time to update this script next year.
Right-clicking on the comments editor brings up a popup menu that allows you to modify the basic typographical settings of the currently selected text (bold, italic, underline).