legend: Understand behavior (and difference) of "-C" and "-F+c" about gmt

[PaulWessel]

Good question. Looking at the code we determine the size of the legend box in two different ways:

1. Via -D+wwidth[/height] which specifically determines the dimensions. Here, height is set to width if not given (square legend box).
2. With no explicit dimensions given then we determine the required dimensions using PostScript operators based on the contents of the label and create the PostScript parameters PSL_legend_label_width and PSL_legend_box_height. These are then used internally to draw the box.

Now, the -Cdx[/dy] option can be used to extend the box in two ways. I will update the doc syntax to show that dx is optional and set to dx if not given, like in most places in GMT.

Then we have the -F+cclearance modifier which seems to overlap with -C here. Certainly, makes little sense to me to allow both at the same time. I think the intent for +c was to allow more flexibility in even adding specific clearance that differ on all four sides. Perhaps adding space where a color bar might fit.

I will test the behaviour of not allowing both -C and -F+c in the same command. I think that is the only sensible solution since -C cannot fully replicate +c's flexibility anyway.

[Esteban82]

This was fixed by #8305, right?

[PaulWessel]

Yes