Margin numbers should be offset by 1

(In the hope that one day this project will have activity again...)

Many coding projects out there have a limit on the number of columns, usually 80 or 100. You might have a personal preference for text files you create, such as 72 columns.

In order to achieve this, you have to invoke Ctrl+T R (Right margin) and set the 1 higher number, e.g. 81, 101 or 73 in the above examples.

This current off-by-one makes no sense whatsoever to me and should be eliminated (also for the left margin).

There are two possible strategies for counting the columns, i.e. actual character positions. Average humans prefer to count items beginning at 1, computer engineers tend to prefer to count items from 0. For text file lines and columns, the 1-based approach is widespread (and rest assured, I'm not asking to change that).

The thinking behind the current numbering could be that e.g. a margin of 81 means that the 81st column (in 1-based numbering) is the first column that already belongs to a margin, i.e. not filled with data. However, the left margin defaulting to 1 instead of 0 does not match this logic.

More importantly, I don't think that the margin is a character column. To me this thinking makes no sense, and it leaves open the question whether we're talking about the last item that's still this, or the first item that's already that, which question has no intuitive answer; moreover whether to express that in 0-based or 1-based numbering. No, the margin is not a character column. The margin is a thin invisible vertical boundary between two character columns.

And no matter if you prefer to count the items from 0 or 1 (both are reasonable choices), counting the boundaries between the items has only one way of counting that makes sense, and that is to use the value of 0 for the starting position (i.e. before the first item -- in the regular human meaning of "first"), and to always denote the number of items you've skipped through.

A regular text file that spans 80 columns should belong to left margin 0, right margin 80. A text file that begins with 2 spaces in every row, followed by up to 70 characters, should have a left margin or 2 and a right margin of 72. And so on.