diff --git a/lib/plan-builder.js b/lib/plan-builder.js
index 26383789..bb0fbb2a 100644
--- a/lib/plan-builder.js
+++ b/lib/plan-builder.js
@@ -66,6 +66,15 @@ bldrgen.AccessPlan.prototype.col = function(...args) {
   return new bldrgen.PlanColumn('op', 'col', checkedArgs);
 };
 
+/**
+  * This function creates a placeholder for a cts query value bound at request time, for use as a
+  * sub-query or argument within a cts query tree (e.g. cts.andQuery, cts.orQuery, cts.wordQuery,
+  * cts.collectionQuery). Distinct from planBuilder#param, which creates an op-namespaced placeholder.
+  * @method planBuilder.cts#param
+  * @since 4.2.0
+  * @param { XsString } [name] - The name of the parameter.
+  * @returns { CtsParam }
+  */
 bldrgen.CtsExpr.prototype.param = function(...args) {
   const paramdef = ['name', [types.XsString], true, false];
   const checkedArgs = bldrbase.makeSingleArgs('cts.param', 1, paramdef, args);