The leftmost column is "locked" in position, meaning that it does not scroll horizontally with the other columns in the table. If the row header is enabled, then two items labeled Lock and Unlock appear in the column menu. These can be used to add or remove additional columns from the non-scrolling row header area.
If the row header is enabled, at least one column must remain locked.
Column locking is NOT reflected in an export to HTML and Excel.