Re: [w3ctag/design-reviews] Review Request - Decentralized Identifiers (DIDs) v1.0 (#556)

> Right - it is impossible to parse a did w/o access to every single did method.

@TomCJones after thinking this through, I don't think this is correct. You can absolutely parse a DID into its method-name and method-specific-id components, without necessarily understanding the method-specific-id. The same is true for URNs, you can parse a URN into its components, without necessarily understanding the NSS (which BTW can also contain an arbitrary number of colons). See this part from [RFC8141](https://tools.ietf.org/html/rfc8141#page-21):

```
   Because the colon character (":") is used to separate "urn" from the
   NID and the NID from the NSS, it's tempting to think of the entire
   URN as being structured by colon characters and to assume that colons
   create a structure or hierarchy within the NSS portion of the URN.
   Such structure could be specified by a particular NID specification,
   but there is no implicit structure.  In a URN such as

      urn:example:apple:pear:plum:cherry

   the NSS string is "apple:pear:plum:cherry" as a whole, and there is
   no specific meaning to the colon characters within that NSS string
   unless such meaning is described in the specification of the
   "example" namespace.
```

This is very consistent with how additional colons in a DID's method-specific-id are understood, see this language in [DID Core](https://w3c.github.io/did-core/#method-schemes):

```
The meaning of colons in the method-specific-id is entirely method-specific. Colons might
be used by DID methods for establishing hierarchically partitioned namespaces, for
identifying specific instances or parts of the verifiable data registry, or for other purposes.
Implementers are advised to avoid assuming any meanings or behaviors associated with
a colon that are generically applicable to all DID methods. 
```


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