SAX-ext proposal #4: feature/property discovery

[David Brownell <david-b@pacbell.net>]

Feature/Property discovery

- There's no way to find out what features a given XMLReader recognizes.

  Given an XMLReader, it's basically possible to find out what values
  it supports (modulo when-to-set sequencing constraints) since they
  can only be true or false (and might be read-only).

- Similarly with properties, though there's no way to determine the
  range of values.

PROPOSAL:

    - Define a new standard property ID:

 http://xml.org/sax/properties/supported-features
   Read-only

   Returns an array of Strings for all the features
   supported by this XMLReader.
    
    - Define a new standard property ID:

 http://xml.org/sax/properties/supported-properties
   Read-only

   Returns an array of Strings for all the properties
   supported by this XMLReader.

[ Mentioned by Miles Sabin; also, Xerces has an API-centric solution ]