PAGE-XML export: negative Coords points values

[memowe]

According to the Ground Truth Guidelines PAGE-XML specification, the points attribute of Coord elements can only contain non-negative integer pairs:

Attribute pc:CoordsType / @points

[...]

pattern	([0-9]+,[0-9]+ )+([0-9]+,[0-9]+)

Pero produces negative values. What specification is Pero using?

[memowe]

Maybe these guidelines are heavily simplified, I don't know enough about this standard.

We managed to parse Coord points including negative coordinates, but to log warnings, it would be nice to know if these are allowed in any way