some more jsdoc

src/vs/editor/common/modes.ts

@@ -395,6 +395,11 @@ export interface CompletionItem {
 	 * is used.
 	 */
 	filterText?: string;
+	/**
+	 * Select this item when showing. *Note* that only one completion item can be selected and
+	 * that the editor decides which item that is. The rule is that the *first* item of those
+	 * that match best is selected.
+	 */
 	preselect?: boolean;
 	/**
 	 * A string or snippet that should be inserted in a document when selecting

src/vs/monaco.d.ts

@@ -4715,6 +4715,11 @@ declare namespace monaco.languages {
 		 * is used.
 		 */
 		filterText?: string;
+		/**
+		 * Select this item when showing. *Note* that only one completion item can be selected and
+		 * that the editor decides which item that is. The rule is that the *first* item of those
+		 * that match best is selected.
+		 */
 		preselect?: boolean;
 		/**
 		 * A string or snippet that should be inserted in a document when selecting