On this page:
get-pasteboard
add-child
delete-child
is-shown?

(send an-alignment-parent get-pasteboard)
  (is-a?/c pasteboard%)
The pasteboard that this alignment is being displayed to.

(send an-alignment-parent add-child child)  void?
  child : (is-a?/c alignment<%>)
Add the given alignment as a child after the existing child.

(send an-alignment-parent delete-child child)  void?
  child : (is-a?/c alignment<%>)
Deletes a child from the alignments.

(send an-alignment-parent is-shown?)  boolean?
True if the alignment is being shown (accounting for its parent being shown).