host environments typically don't have access to the respective macro
function (cf. 04b8eda2c18c8b1ff0c5d1a7647f323763ec2dfb) - so for views'
entry points, we need a way to identify macros via strings after all

in the process, added support for HTML fragments (as opposed to
documents; fragments omit the doctype and typically also omit layout,
though the latter is up to the respective entry-point macro)