Function conforms 

pub fn conforms<'a>(
    parent: &Reader<'a>,
    element: &Element<'a>,
    field: &'static str,
) -> Result<()>

Whether a range and everything under it is DER.

Definite lengths in their shortest form, primitive encodings where the distinguished rules require them, assigned universal types, and the members of a set in ascending order of their encodings (X.690 11.6).

The reader decides which rules apply to the outermost header, so a caller holding a range to DER inside a BER document reads it again under DER first; structured_asn1::Reader::reread is what that is for.

Errors

Reports which rule was broken and where.