diff --git a/question/classes/local/bank/condition.php b/question/classes/local/bank/condition.php
index 549446a1d52..4ad66b53a72 100644
--- a/question/classes/local/bank/condition.php
+++ b/question/classes/local/bank/condition.php
@@ -59,11 +59,14 @@ abstract class condition {
     }
 
     /**
-     * Extract the required filter from the provided question bank view.
+     * Extract the required filter from the provided question bank view and set the initial values.
      *
-     * This will look for the filter matching {@see get_condition_key()}
+     * This will look for the filter matching {@see get_condition_key()} in the view's current filter parameter.
+     * If the filter is not being initialised to display the question bank UI (for example, to resolve a list of questions matching
+     * a set of filters), then the `$qbank` argument may be null, and any usage of it to set the initial filter state is skipped.
      *
-     * @param view|null $qbank
+     * @param ?view $qbank The question bank view the filter is being rendered for. This may only be used for setting the
+     *     initial state of the filter.
      */
     public function __construct(?view $qbank = null) {
         if (is_null($qbank)) {
diff --git a/question/classes/local/bank/plugin_features_base.php b/question/classes/local/bank/plugin_features_base.php
index cdb24ed23c6..3644bcc5344 100644
--- a/question/classes/local/bank/plugin_features_base.php
+++ b/question/classes/local/bank/plugin_features_base.php
@@ -109,7 +109,14 @@ class plugin_features_base {
     /**
      * Return search conditions for the plugin.
      *
-     * @param view|null $qbank
+     * This is used by question bank view classes to get the list of available filters to display in the filter UI.
+     *
+     * This is also used to get the list of available filters for other purposes, for example resolving the list of questions
+     * selected by a set of filters, in which case the `$qbank` argument may be `null`
+     * {@see filter_condition_manager::get_condition_classes()}.
+     *
+     * @param view|null $qbank The current question bank view the filters are being rendered for, for example the main question
+     *     bank page, or the random question view.
      * @return condition[]
      */
     public function get_question_filters(?view $qbank = null): array {