     }
 
     /**
-     TODO: docstring
+     Replaces note at `collectionIndex`.
+     
+     - parameter collectionIndex: Note collection index.
+     - parameter noteCollection: `NoteCollection` to replace note.
+     - parameter setIndex: Note set index.
+     - throws:
+        - `MeasureError.internalError`
      */
     internal mutating func replaceNote(at collectionIndex: NoteCollectionIndex, with noteCollections: [NoteCollection], inSet setIndex: Int) throws {
         guard let tupletIndex = collectionIndex.tupletIndex else {

    }

    /**
     TODO: docstring
     
     - parameter index: The index of the note in the specified note set.
     - parameter setIndex: The index of the note set holding the note.

    }

    /**
     Calculates the note collection indexes stored in the measure.
     */
    private mutating func recomputeNoteCollectionIndexes() {
        noteCollectionIndexes = [[NoteCollectionIndex]]()
