clarify workflow step parameters

Author: jmchilton

Workflow.yml

@@ -49,6 +49,8 @@ $graph:
       ## Changelog
 
         * Clarify how Requirements are inherited by step processes
+        * Clarify behavior around step inputs not consumed by the target
+          run process.
         * Document explicitly that CWL allows pass-through of workflow inputs to outputs
         * Added optional name and doc fields to OutputRecordSchema
         * Default values for some fields are now expressed in the schema
@@ -263,7 +265,11 @@ $graph:
   doc: |
     The input of a workflow step connects an upstream parameter (from the
     workflow inputs, or the outputs of other workflows steps) with the input
-    parameters of the underlying step.
+    parameters of the process specified by the `run` field. Only input parameters
+    declared by the target process will be passed through at runtime to the process
+    though additonal parameters may be specified (for use within `valueFrom`
+    expressions for instance) - unconnected or unused parameters do not represent an
+    error condition.
 
     ## Input object