Other Graph XML specifications/formats

I understand that GEXF's design is mostly done around Gephi, nonetheless, it may be a good idea to try to keep track of other Graph XML formats providing similar support. This could bring ideas about needed/desired features for both GEXF and Gephi. Here are a few examples:

- **DGML**: Directed Graph Markup Language ([link](https://docs.microsoft.com/en-us/visualstudio/modeling/directed-graph-markup-language-dgml-reference?view=vs-2022))
- **GraphML** ([link](http://graphml.graphdrawing.org/))
- **DGML**: Directed Graph Markup Language ([link](https://en.wikipedia.org/wiki/DGML))
- **XGMML**: eXtensible Graph Markup and Modeling Language ([link](https://web.archive.org/web/20140329092403/http://cgi5.cs.rpi.edu/research/groups/pb/punin/public_html/XGMML/))

XML formats used in Phylogenetics (some interesting features to consider for GEXF)

- **PhyloXML** ([link](http://www.phyloxml.org/#:~:text=phyloXML%20(example)%20is%20an%20XML,gene%20duplication%20and%20speciation%20events.))
- **NeXML** ([link](http://www.nexml.org/))

Start by reviewing the linked DGML, GraphML, XGMML, PhyloXML, and NeXML specifications and compare their features with GEXF. The issue does not name repository files or tests; clarify the intended output and scope before starting. Done should be a maintained comparison or documented set of relevant ideas for GEXF and Gephi.

Written by the indexing model from the issue text.