Right now the default is to wrap markup if the line becomes too long. It would be very nice to have a horizontal scroll bar (in addition to the vertical one already there) on the markup editing window. Making this optional would be fine.

This problem is particular bad when dealing with large tables that have a lot of links in them... the resulting lines end up making hard-to-read table markup even harder to read. To deal with this I often end up copying my markup over to a non-wrapping editor, editing it there, then pasting it back.