[gtk+/gtk-3-22] css-overview: Fix+Explain color expr number ranges

[Daniel Boles <dboles src gnome org>]

commit b73e6ffbd852fef3f1982239985fd70d85a69bba
Author: Daniel Boles <dboles src gnome org>
Date:   Sat Mar 18 01:13:42 2017 +0000

    css-overview: Fix+Explain color expr number ranges
    
    Last try, promise. They don’t all use 0 to 1. We should probably explain
    the effects too. Hopefully this manages that while not being too verbose

 docs/reference/gtk/css-overview.xml |   12 ++++++++----
 1 files changed, 8 insertions(+), 4 deletions(-)
---
diff --git a/docs/reference/gtk/css-overview.xml b/docs/reference/gtk/css-overview.xml
index 6e4f4b0..0706f16 100644
--- a/docs/reference/gtk/css-overview.xml
+++ b/docs/reference/gtk/css-overview.xml
@@ -584,12 +584,16 @@ background-color: @bg_color;
     <para>
       GTK+ also supports color expressions, which allow colors to be transformed
       to new ones and can be nested, providing a rich language to define colors.
+      Color expressions resemble functions, taking 1 or more colors and in some
+      cases a number as arguments.
     </para>
     <para>
-      Color expressions resemble functions, taking 1 or more colors and in some
-      cases a number as their arguments. The number is floating-point, clamped
-      between 0 and 1, and specifies the degree to which the expression will
-      transform the given color(s) in the manner that is indicated by its name.
+      shade() leaves the color unchanged when the number is 1 and transforms it
+      to black or white as the number approaches 0 or 2 respectively. For mix(),
+      0 or 1 return the unaltered 1st or 2nd color respectively; numbers between
+      0 and 1 return blends of the two; and numbers below 0 or above 1 intensify
+      the RGB components of the 1st or 2nd colour respectively. alpha() takes a
+      number from 0 to 1 and applies that as the opacity of the supplied color.
     </para>
 
 <literallayout><code>〈color expression〉 = lighter(〈color〉) | darker(〈color〉) | shade(〈color〉,〈number〉) | 
alpha(〈color〉,〈number〉) | mix(〈color〉,〈color〉,〈number〉)</code>