You must supply an expr attribute containing an expression that is evaluated to generate the output src (5.2.7.3) attribute of the <img> tag.
For example:
>>> import albatross >>> ctx = albatross.SimpleContext('.') >>> ctx.locals.src = 'httpicons.r.us/spam.png' >>> albatross.Template(ctx, '<magic>', ''' ... <al-img expr="src" whitespace> ... ''').to_html(ctx) >>> ctx.flush_content() <img src="httpicons.r.us/spam.png">