Its a cheap n easy way to draw a straight line directly back to the last place the pen was set down probably the last M or m command. The fill operation fills open subpaths by performing the fill operation as if an additional closepath command were added to the path to connect the last point of the subpath with the first point of the subpath. Apparently there is no difference between the uppercase and lowercase command.
H horizontal lineto.
Strokes are drawn centered around the path. The following commands are available for path data. You can see the magic happening in this pen. Active Oldest Votes.