**(hsla: // [[harlowe:Number|Number]], Number, Number, Number//) -> //[[harlowe:Colour|colour]]//**

A special version of [[harlowe:hsl|(hsl:)]], this macro allows you to supply not just the hue (h) angle in
degrees, saturation (s) and lightness (l) percentages, but also the transparency
(alpha, or a) percentage, which is a fractional value between 0 (fully transparent)
and 1 (fully visible).

Anything drawn with a partially transparent [[harlowe:colour|colour]] will itself be partially transparent. You
can then layer such elements to produce a few interesting visual effects.

=== Example usage: ===

''%%(hsla: 120, 0.5, 0.8, 0.6)%%'' produces a 40% transparent faint green.

=== Details: ===

This macro takes the same range of [[harlowe:number|number]] as the CSS ''%%rgba()%%'' function.

Giving alpha percentages higher than 1 or lower than 0 will cause an error.

=== See also: ===

[[harlowe:rgb|(rgb:)]], [[harlowe:rgba|(rgba:)]], [[harlowe:hsl|(hsl:)]]