[luatex] Q: What is a "running" glue dimension in rule node?

[Patrick Gundlach]

Good morning,

I have this rule in a vbox:

\vrule width 1mm

and this looks like it turns out to a node like this:

rule: width=186467, height=-1073741824, depth=-1073741824

Now looking at the reference manual, it states (8.1.2.3) that the special value "-1073741824" is used for ‘running' glue dimensions. What is a running glue dimension? Does that mean that there is no height and depth given in TeX's input?

Patrick