Looking for SAML 1.x AuthnRequest web flow specification

[shibboleth655 at lewenberg.com]

The binding

<SingleSignOnService 
Binding="urn:mace:shibboleth:1.0:profiles:AuthnRequest" 
Location="https://idp.example.org/idp/profile/Shibboleth/SSO" />

appears in an IdP's metadata to indicate, as I understand it, that the 
IdP supports SAML 1.x non-Idp-initiated web flow. Is that correct? In 
any case, where can I find documentation that defines this flow?

Thanks