Append new text at specified address, or at present address if none is specified. Add a ! to switch the autoindent setting that will be used during input (e.g., if autoindent was enabled, ! disables it). Enter new text after entering the command. Terminate input of new text by entering a line consisting of just a period.
aBegin appending to current line.
Append this line
and this line too.
.Terminate input of text to append.