Whenever "KeepIndent" mode is on the current indent value is added to the start of each line. The default extra indent is none.
The "IndentCmd" parameter is a rexx command which produces a string value which will be used for extra indenting.
The following command would increase any indenting by 10 spaces for following lines:
#option ExtraIndent=^copies(' ', 10)^ KeepIndent=ON