Returns the object that indicates how the halo area around the text
should be filled.
The default halo fill is solid white (Color
“#FFFFFF”). The glyph’s fill is plotted on top of the halo. The default font fill is solid
black (Color “#000000”).
Returns the expression that will be evaluated to get the pixel radius of
the halo around the text.
The Radius element gives the absolute size of a halo radius in pixels encoded as a
floating-point number. The radius is taken from the outside edge of a font glyph to extend
the area of coverage of the glyph (and the inside edge of “holes” in the glyphs). The halo
of a text label is considered to be a single shape. The default radius is one pixel.
Negative values are not allowed.