Used (only) by export codes that create link lists and action code links().
The designator source refers to the note from which the exported links will arise. In most (all?) cases this equates to both this and current, so the object 'source' makes it easier for the user to specify generically from where data is drawn.
See also - destination.
For example,
^basicLinks("<ul>","<li>^value($Name(source))^ - > ","</li>","</ul>")^
will export a list of links, each target note's Name preceded by the source note's name and a -> pointing to the target note's name.
Note that the designator can be used in the link export code's item prefix and/or suffix arguments but this designator can't be used with ^value^ and attribute references. Meanwhile, the link's anchor text always remains the Name (i.e. title) of the link's target note, linked to that note's page's URL.
