Document the input to an attribution function

src/ol/source/Source.js

@@ -7,8 +7,8 @@ import {abstract} from '../util.js';
 import {get as getProjection} from '../proj.js';
 
 /**
- * A function that returns a string or an array of strings representing source
- * attributions.
+ * A function that takes a {@link module:ol/PluggableMap~FrameState} and returns a string or
+ * an array of strings representing source attributions.
  *
  * @typedef {function(import("../PluggableMap.js").FrameState): (string|Array<string>)} Attribution
  */