Inherited methods:
from alignment-parent<%>
add-child
delete-child
get-pasteboard
is-shown?
from alignment<%>
align
get-min-height
get-min-width
get-parent
set-min-sizes
show
show/ hide
stretchable-height
stretchable-width
from dllist<%>
for-each
map-to-list
next
prev

(new horizontal-alignment% [parent parent] 
  [[show? show?] 
  [after after]]) 
  (is-a?/c horizontal-alignment%)
  parent : (is-a?/c alignment-parent<%>)
  show? : boolean? = #t
  after : (or/c (is-a?/c alignment<%>) false/c) = #f
Inserts a new horizontal-alignment container into parentoptionally after a given container also in parent. The new container can be initially shown or hidden.