> The first is that the format isn't really parseable without using a schema, unlike (say) XML or JSON.
You can parse DER without using a schema (except for implicit types, although even then you can always parse the framing even if the value cannot necessarily be parsed; for this reason I only use implicit types for sequences and octet strings (and only if an implicit type is needed, which it often isn't), in my own formats). (The meaning of many fields will not be known without the schema, but that is also true of XML and JSON.)
I wrote a DER parser without handling the schema at all.
You can parse DER without using a schema (except for implicit types, although even then you can always parse the framing even if the value cannot necessarily be parsed; for this reason I only use implicit types for sequences and octet strings (and only if an implicit type is needed, which it often isn't), in my own formats). (The meaning of many fields will not be known without the schema, but that is also true of XML and JSON.)
I wrote a DER parser without handling the schema at all.