diff --git a/Documentation/ProjectFile/prj/parameters/parameter/Function/t_expression.md b/Documentation/ProjectFile/prj/parameters/parameter/Function/t_expression.md
index f9eaacbf26b6efa4cedc4acaa0d3cc050bd96ea7..823536ab6268685d048feda0048b66cd905384cc 100644
--- a/Documentation/ProjectFile/prj/parameters/parameter/Function/t_expression.md
+++ b/Documentation/ProjectFile/prj/parameters/parameter/Function/t_expression.md
@@ -1 +1,6 @@
-Mathematical expression of the function (currently x,y,z, and t are supported variables). For non-scalar values, an expression should be given for each component.
+Mathematical expression of a function.
+For non-scalar values, an expression should be given for each component.
+
+Currently x,y,z, and t are supported variables, and curves from the `<curves>`
+section can be called using their names.  A curve is a single argument function
+and can be used in an expression like `curveA(sin(t))`.