HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part II

EN LA, Line Attributes 22-17
Note Labels are always drawn with rounded ends and joins.
Line Ends
The value you specify for line ends determines how the ends of line
segments are shaped. The following illustration describes the four
types of line ends.
Figure 22-11Four Line Ends
Line Joins
The value you specify for the line joins attribute determines how
connecting line ends (corners) are shaped. The following illustration
describes the five types of line joins. If the first and last points of a
series of lines are the same, they join according to the current line
join and miter limit.