5.3.6.2 expr="..." attribute

This attribute must the specified. It contains an expression that is evaluated when the template is executed and the result is written as a string to the output.

For example:

>>> import albatross
>>> ctx = albatross.SimpleContext('.')
>>> albatross.Template(ctx, '<magic>', '''
... hash('spam') is <al-value expr="hash('spam')" whitespace>
... ''').to_html(ctx)
>>> ctx.flush_content()
hash('spam') is 1626740519