non-standard GraphML syntax for directed edges

[nichtich]

GraphML edges are directed depending on edge attribute directed set to graph attribute edgedefault by default. Graphonline uses edge attribute isDirect instead and ignores graph attribute edgedefault. To maintain backwards compatibility, I'd recommend to support all three:

• directed (primary)
• isDirect (fallback)
• edgedefault (else)

P.S: I'm surprised the source code emits proper GraphML but the "export" feature at https://graphonline.ru/en/ returns a slightly different format with isDirect XML attribute?!

P.P.S: I think this code is doing the wrong conversion from internal graph data to GraphML.

[UnickSoft]

Thanks. We will look it. Indeed we have 2 exports for graphoffline utility and for user export.

[UnickSoft]

Fixed.