Double association between node is not supported

[binout]

Class diagram Domain

digraph G {
graph [labelloc=top,label="Domain",fontname="Verdana",fontsize=12];
edge [fontname="Verdana",fontsize=9,labelfontname="Verdana",labelfontsize=9];
node [fontname="Verdana",fontsize=9,shape=record];
c1 [label="Quantity"]
c2 [label="Size"]
c1 -> c2 [label="size" , ];

// with API it's not possible to add a 2nd association between c1 and c2 with another label ...
c1 -> c2 [label="mainSize"  , ];

}

[cyriux]

In my usage it was a feature to be able to add nodes and associations without checking for duplicates and having dot-diagram de-deplicate for me. Could keep that with an equality that includes the comment?