code: private void parseEnumeration(boolean isNames) throws Exception {
          dataBufferAppend('(');
  
          // Read the first token.
          skipWhitespace();
          dataBufferAppend(readNmtoken(isNames));
          // Read the remaining tokens.
          skipWhitespace();
          while (!tryRead(')')) {
              require('|');
              dataBufferAppend('|');
              skipWhitespace();
              dataBufferAppend(readNmtoken(isNames));
              skipWhitespace();
          }
          dataBufferAppend(')');
      }
docs: Parse an enumeration.
  
  <pre>
  [59] Enumeration ::= '(' S? Nmtoken (S? '|' S? Nmtoken)* S? ')'
  </pre>
  
  <p>
  NOTE: the '(' has already been read.