Undo
Once any changes have been made to a web page in the editor, the undo function becomes available, as indicated by the bright icon. Thereafter, you may undo the changes.  There are up to 20 undo levels.  Any function that you perform, i.e. justifying text, bolding text, or adding an image will automatically create an undo level.  If you are simply typing text, the undo function takes a snapshot of the content every five to six seconds, providing the ability to undo text changes.

The "grayed out" icon for the undo function displays when there have been no updates or changes made to the document. As there are no changes to undo; the feature is "unavailable".

Redo
Once you have "undone" a change using the undo function, the redo button becomes active.  This enables you to revert the document to the way it was prior to the undo.

The "grayed out" icon for the redo function displays when there have been no undo changes made to the document. Unless and until an undo has been executed, there are no redo changes possible and the grayed out icon will display.

Important: The undo and redo functions are reset and the ability to undo or redo page editing to revert to previous edit stages is eliminated once a document is saved or when one navigates to another page.