Inserts tabulator at the position of caret.
function InsertTab: Boolean;
(introduced in v1.9)
Inserted tabulator has the current text and the current paragraph style.
This method always inserts a tabulator, regardless of RVStyle.SpacesInTab mode.
If RVStyle.SpacesInTab=0, this method does the same work as InsertText(#9).
Method type: 
editing-style method for insertion.
Return value:
True if the insertion was successful (it can fail due to protection, or when inserting in table having multicell selection)
See also method of TRichView:
▪AddTab.