put comment about expression

git-svn-id: http://svn.osgeo.org/postgis/trunk@8136 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/reference_raster.xml b/doc/reference_raster.xml
index f195bf8d8054a07a5886ba46b27c2377b39e3921..d347467b490c47d92f623c33c488e5b2b80f5206 100644 (file)
--- a/doc/reference_raster.xml
+++ b/doc/reference_raster.xml
@@ -5312,7 +5312,7 @@ WHERE rid=167;
                                <variablelist>
                                        <varlistentry>
                                                <term>expression</term>
-                                               <listitem><para>The algebraic expression involving the 2 rasters that will define the pixel value when pixels intersect</para></listitem>
+                                               <listitem><para>A PostgreSQL algebraic expression involving the 2 rasters and PostgreSQL defined functions/operators that will define the pixel value when pixels intersect. e.g. ((rast1 + rast2)/2.0)::integer</para></listitem>
                                        </varlistentry>
                                        <varlistentry>
                                                <term>pixeltype</term>