This is simply a proposal to have commonly available market-data made accessible as XML somewhere, so that it can be accessed by LSL scripts, or external sites, more easily, and independently of any changes to the web-site(s) themselves.
So for example, I might be able to access some standard URL and get the following value:
<?xml version='1.0' encoding='UTF-8'?>
<MarketData timestamp="123456789">
<LindexExchangeRates>
<LindexExchangeRate currency="USD">270.12345</ExchangeRate>
<LindexExchangeRates>
</MarketData>
This way to fetch information on US dollars, I just look up the LindexExchangeRate tag for "USD" and pull the value from that. This way it's nice and standardised.