5.3.8.7 prepare attribute

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5.3.8.7 `prepare` attribute

This attribute allows you to place pagination controls before the formatted sequence content.

When the `prepare` attribute is present the `<al-for>` tag will perform all processing but will not write any output. This allows you to test pagination results before presenting output.

For example:

    >>> import albatross
    >>> class Ctx(albatross.SimpleContext, albatross.HiddenFieldSessionMixin):
    ...     def __init__(self):
    ...         albatross.SimpleContext.__init__(self, '.')
    ...         albatross.HiddenFieldSessionMixin.__init__(self)
    ...
    >>> ctx = Ctx()
    >>> albatross.Template(ctx, '<magic>', '''
    ... <al-for iter="i" expr="range(500)" pagesize="20" prepare/>
    ... <al-if expr="i.has_prevpage()"> prev</al-if>
    ... <al-if expr="i.has_nextpage()"> next</al-if>
    ... <al-for iter="i" pagesize="20" whitespace="indent">
    ...  <al-value expr="i.value()">
    ... </al-for whitespace>
    ... ''').to_html(ctx)
    >>> ctx.flush_content()
     next 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Note the XML empty tag syntax on the `<al-for prepare>` tag.