Alignment is accepted in restricted mode when doctype is set to HTML5 :
  setup:
    setRestricted: true
    setLite: false
    setImages: true
    setLinkRelationShip: nofollow
  input: |
    !=10x10.gif!

    !>10x10.gif!

    !<10x10.gif!

  expect: |
    <p><img alt="" class="align-center" src="10x10.gif" /></p>

    <p><img alt="" class="align-right" src="10x10.gif" /></p>

    <p><img alt="" class="align-left" src="10x10.gif" /></p>

In XHTML same generates align attribute:
  setup:
    setRestricted: true
    setLite: false
    setImages: true
    setLinkRelationShip: nofollow
    setHtmlType: xhtml
  input: |
    !=10x10.gif!

    !>10x10.gif!

    !<10x10.gif!

  expect: |
    <p><img align="center" alt="" src="10x10.gif" /></p>

    <p><img align="right" alt="" src="10x10.gif" /></p>

    <p><img align="left" alt="" src="10x10.gif" /></p>