F11 Margin

If the left margin is set to column one (flush left), press F11 to reset the margin to the current cursor position. If the left margin is set to a column other than one (flush left), press F11 to reset the margin to column one. If you position the cursor at column one and you are editing a UNIX text file, a continuation character (background colon :) displays. This allows text lines longer than the window line to be stored as one record.

From the Dictionary-IV User Guide, version 8.9.1. Open this page in the PDF