Please consider producing a revised MIME resolver DTD that would be easier to
understand. Even after having used it, I cannot remember how it is supposed to
work without referring to the docs, and even then it is hard to follow. There
would be no compatibility problem with making a new DTD since we would just
provide a different processor.

Problems with the current version (syntactic, not feature complaints):

1. <exit/> or <resolver mime="null"/>: first, there ought not be equivalent ways
of saying the same thing, this just increases confusion. Second, does this exit
out of the entire <MIME-resolver>? If so, it is not clearly documented to do so.

2. <MIME-resolver> is mixed-case whereas all other elements and attrs are
lower-case.

3. <file> is an odd name for one rule.

4. Why are most rules children of <file> but <xml-rule> is a child of
<resolver>? This seems very counterintuitive. If you have resolved it, why are
there then more rules inside? Why not just make <pi>, <doctype>, and <element>
children of <file> like other things?

5. It is not obvious when reading things what is conjunctive and what
disjunctive. I.e. it seems that at least one rule beneath <file> must match -
disjunction. It does not appear to be document in the case of <xml-rule>. It
would be hard to guess what was meant without carefully reading DTD
documentation. This is perhaps the major thing.

6. Messy that ns can be an attr or child of <element> - pick one (child) and
stick to it.

Suggest a more uniform syntax based more on boolean logic, such as:

<mime-resolver>
  <resolver mime="text/x-ant+xml">
    <and>
      <ext name="xml"/>
      <xml-element name="project">
        <attr name="default"/>
      <xml-element>
    </and>
  </resolver>
</mime-resolver>

It would be much easier to understand what was meant IMHO. Minor changes would
work intuitively, e.g. match a different extension too but check in XML:

<mime-resolver>
  <resolver mime="text/x-ant+xml">
    <and>
      <or>
        <ext name="xml"/>
        <ext name="ant"/>
      </or>
      <xml-element name="project">
        <attr name="default"/>
      <xml-element>
    </and>
  </resolver>
</mime-resolver>

vs. match a different extension and trust it:

<mime-resolver>
  <resolver mime="text/x-ant+xml">
    <or>
      <and>
        <ext name="xml"/>
        <xml-element name="project">
          <attr name="default"/>
        <xml-element>
      </and>
      <ext name="ant"/>
    </or>
  </resolver>
</mime-resolver>

cancel with file attrs:

<mime-resolver>
  <exit>
    <fattr name="not-ant" text="true"/>
  </exit>
  <resolver mime="text/x-ant+xml">
    <and>
      <ext name="xml"/>
      <xml-element name="project">
        <attr name="default"/>
      <xml-element>
    </and>
  </resolver>
</mime-resolver>

Something more like Lisp might even be better:

<mime-resolver>
  <if>
    <test><fattr name="not-ant" text="true"/></test>
    <then><fail/></then>
    <else>
      <if>
        <test>
          <and>
            <ext name="xml"/>
            <xml-element name="project">
              <attr name="default"/>
            <xml-element>
          </and>
        </test>
        <then><succeed mime="text/x-ant+xml"/></then>
        <else><fail/></else>
      </if>
    </else>
  </if>
</mime-resolver>

where

% rule = fattr | ext | xml-element | ...
% boolterm = %rule; | and | or | not
% mimeterm = succeed | fail | if
mime-resolver: (%mimeterm;)
if: (test, then, else)
test: (%boolterm;)
then: (%mimeterm;)
else: (%mimeterm;)
and: (%boolterm;)+
or: (%boolterm;)+
not: (%boolterm;)
succeed: EMPTY; ATTLIST: mime
fail: EMPTY