Internal Editor Locks

Instances of editor<%> have three levels of internal locking:

• write locking -- When an editor is interally locked for writing, the abstract content of the editor cannot be changed. However, snips in a text editor can still be split and merged, and the text editor can be changed in ways that affects the flow of lines.
• flow locking -- When a text editor is interally locked for reflowing, it is locked for writing and the actual snip content of the editor cannot change. Thus, no change can be made that would affect the flow of lines in the editor.
• read locking -- When an editor is interally locked for reading, no operations can be performed on the editor. This extreme state is used only during callbacks to its snips while the editor is in a sensitive state.