Line markers are simple shapes placed regularly along a path. This can be useful for giving directional arrows or marking distance at a set interval.

If markerUnits is not specified, it defaults to "strokeWidth" This means that 1 in a marker is equivalent to the strokeWidth of the graphic that the marker is applied to.

An arrow marker can be handy if you're trying to work with a fill rule the evenOdd rule is confusing.

You may think, like I did, that a marker would be a great user interface element to tie some scripting behaviour to. In my case I thought it would be a clever place to have a user click in order to move a vertex. Unfortunately, the specification explicitly states that "Event attributes and event listeners attached to the contents of a 'marker' element are not processed; only the rendering aspects of 'marker' elements are processed." To me, this doesn't leave a whole lot of good uses for markers outside the originally intended use as a generic arrowhead. I'd recommend their use when making a callout box but for anything interactive you're going to need a different element.

Marker Example