It is not in Tools > Inspectors > Document > Links, only in Tools > Inspectors > Info > Custom.
If we can move the custom link into Tools > Inspectors > Document > Links, that will be great.
Also, I noticed there is incoming links tab in the Tools > Inspectors > Document > Links, is it actually back links? That is cool!
Another thing, in Tools > Inspectors > Document > Links, I noticed that the outside links and internal links are mixed together, will be great if there are some filters, sort, or some background colours to tell the difference.