I'm pretty sure I already made this comment, but I can't find it, so here it is again.

If you run [arctest](https://gist.github.com/KCErb/b22e47c7cd9259cc1826) you'll get a very strange error:

```
NoMethodError: undefined method `element_end' for nil:NilClass
  report_relative_to_parent_end at /Users/KC/Programming/Shoes/shoes4/lib/shoes/dimension.rb:198
                            end at /Users/KC/Programming/Shoes/shoes4/lib/shoes/dimension.rb:28
                         bottom at /Users/KC/.rvm/rubies/jruby-1.7.12/lib/ruby/1.9/forwardable.rb:201
                         bottom at /Users/KC/.rvm/rubies/jruby-1.7.12/lib/ruby/1.9/forwardable.rb:201
              update_dimensions at /Users/KC/Programming/Shoes/shoes4/lib/shoes/common/style.rb:96
                           each at org/jruby/RubyArray.java:1613
              update_dimensions at /Users/KC/Programming/Shoes/shoes4/lib/shoes/common/style.rb:95
                          style at /Users/KC/Programming/Shoes/shoes4/lib/shoes/common/style.rb:27
                     style_init at /Users/KC/Programming/Shoes/shoes4/lib/shoes/common/style.rb:69
                     initialize at /Users/KC/Programming/Shoes/shoes4/lib/shoes/arc.rb:19
                         create at /Users/KC/Programming/Shoes/shoes4/lib/shoes/dsl.rb:66
                            arc at /Users/KC/Programming/Shoes/shoes4/lib/shoes/dsl.rb:188
                         (root) at /Users/KC/Programming/Shoes/shoes4/local_tests/arc_test.rb:2
                  instance_eval at org/jruby/RubyBasicObject.java:1533
                  execute_block at /Users/KC/Programming/Shoes/shoes4/lib/shoes/app.rb:249
                  execute_block at /Users/KC/.rvm/gems/jruby-1.7.12@shoes/gems/after_do-0.3.0/lib/after_do.rb:99
         create_execution_block at /Users/KC/Programming/Shoes/shoes4/lib/shoes/app.rb:279
                           call at org/jruby/RubyProc.java:271
                     eval_block at /Users/KC/Programming/Shoes/shoes4/lib/shoes/slot.rb:46
                         append at /Users/KC/Programming/Shoes/shoes4/lib/shoes/slot.rb:55
                     eval_block at /Users/KC/Programming/Shoes/shoes4/lib/shoes/app.rb:273
                      setup_gui at /Users/KC/Programming/Shoes/shoes4/lib/shoes/app.rb:148
                     initialize at /Users/KC/Programming/Shoes/shoes4/lib/shoes/app.rb:58
                            app at /Users/KC/Programming/Shoes/shoes4/lib/shoes/app.rb:29
                         (root) at /Users/KC/Programming/Shoes/shoes4/local_tests/arc_test.rb:1
                           load at org/jruby/RubyKernel.java:1081
                         (root) at /Users/KC/Programming/Shoes/shoes4/lib/shoes/cli.rb:1
                    execute_app at /Users/KC/Programming/Shoes/shoes4/lib/shoes/cli.rb:73
                         (root) at /Users/KC/Programming/Shoes/shoes4/bin/ruby-shoes:6
```
I cannot imagine why `:end` is getting passed into dimensions here . . . any suggestions?