5.3.2.1 expr="..." attribute

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5.3.2.1 `expr="..."` attribute

If the `expr` attribute is present it is evaluated when the template is executed to generate the name of a template file. The specified template file is loaded and executed with the output replacing the `<al-include>` tag.

For example:

    >>> open('other.html', 'w').write('name = "<al-value expr="name">"')
    >>> import albatross
    >>> ctx = albatross.SimpleContext('.')
    >>> ctx.locals.name = 'other.html'
    >>> albatross.Template(ctx, '<magic>', '''
    ... Inserting <al-value expr="name">: <al-include expr="name"> here.
    ... ''').to_html(ctx)
    >>> ctx.flush_content()
    Inserting other.html: name = "other.html" here.