From SVG

Big markers have little markers

Upon their paths to bite 'em

And little markers have lesser markers

And so, ad infinitem

In theory, any path or basic shape can have markers. Markers are constrained to the nodes on the path or to put it the other way, the nodes on the path are constrained to be where you want the markers to be. If you want markers, which you almost always don't. Markers take their fill and stroke from where they are defined, not where they are used (but see vector effects. In practice, markers are usually seen on the polyline element. Recursive markers are rarely seen outside of test cases.

Proposal: in SVG2, de-emphasise markers. Possibly deprecate them.

Proposal: add a polyMarker basic shape that is like polyline, with markers, except that the line is not drawn and the markers are children of the polyMarker element. That deals with the 'draw markers at this list of points' 80% use case.