>>> import albatross
>>> ctx = albatross.SimpleContext('.')
>>> albatross.Template(ctx, '<magic>', '''
... <al-macro name="pagelayout">
...  <al-setdefault name="title">Parrot</al-setdefault>
...  <title><al-usearg name="title"></title>
... </al-macro>
... ''').to_html(ctx)
>>> albatross.Template(ctx, '<magic>', '''
... <al-expand name="pagelayout">
...  <al-setarg name="title">Lumberjack</al-setarg>
... </al-expand>''').to_html(ctx)
>>> ctx.flush_content()
<title>Lumberjack</title>
>>> albatross.Template(ctx, '<magic>', '''
... <al-expand name="pagelayout">
... </al-expand>''').to_html(ctx)
>>> ctx.flush_content()
<title>Parrot</title>