Many people have asked questions about customizing or creating user-defined arrow heads:
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but yEd doesn't support that.
I would like user-defined arrow heads, too.
Without user-defined arrow heads, yEd is limited to creating only diagram types that you, the designers, have anticipated. Then users have to ask the developers to create a new arrow head when they need one that wasn't anticipated. If yEd supported user-defined arrow heads, then people could use yEd to create diagram types that weren't previously anticipated, without having to ask the software developers to make a new arrow head for them.
Here is what I would like to see in yEd:
The user can define shapes for new arrow heads. (Importing an SVG file is fine.)
The arrow heads are scaleable, independent of line width. Perhaps the user draws the shape with zero-width lines, and the arrow head inherits the line width from the edge.
The fill color is user-selectable at any time, not fixed to a color defined when the new arrow head is created.
The line color works the way it does already, inherited from the edge.
In addiion to the text label that edges currently have, it would be nice if the user could specifiy text for ends independently, for example, for indicating multiplicity.