     bindingStrength: ->
       4
 
+    # Pretty-print subtraction.
+    #
+    # @param renderFunction [String] What function to render with.
+    # @param plus [String] What plus looks like.
+    # @param minus [String] What minus looks like.
+    # @return [String] Pretty-printed add node.
     drawPretty: (renderFunction, plus, minus) ->
       out = ""
 
-      if @terms[0] instanceof Negate
+      if @terms[0] instanceof prettyRender.Negate
         out += minus
         out += @terms[0].contents[renderFunction]()
       else
         out += @terms[0][renderFunction]()
 
       for term in @terms.slice(1)
-        if term instanceof Negate
+        if term instanceof prettyRender.Negate
           out += minus
           out += term.contents[renderFunction]()
         else

      "<msup>#{@left.renderMathML()}#{@right.renderMathML()}</msup>"

  # Drawing node representing bracketing.
  class Bracket extends DrawingNode

    # Make a new bracket drawing node.
    #
    # @param contents [Array<DrawingNode>] Drawing nodes inside the brackets.
    # @return [Bracket] A new bracket node.
    constructor: (@contents) ->

    # How strongly bound this node is.


define ->

  prettyRender = {}

  # Generic drawing node, parent of all other drawing nodes.
  class prettyRender.DrawingNode

    # Draw the node as a string.
    #
