Abstract from the Draft:
This working draft describes SVG's XML Binding Language (sXBL). sXBL is a mechanism for defining the presentation and interactive behavior of elements described in a namespace other than SVG's.
sXBL is intended to be used to enable XML vocabularies (tag sets) to be implemented in terms of SVG elements. For instance, a tag set describing a flowchart could be mapped to low-level SVG path and text elements, possibly including interactivity and animation.
sXBL is intended to be an SVG-specific first version of a more general-purpose XBL specification (e.g., "XBL 2.0"). The intent is that, in the future, a general-purpose and modularly-defined XBL specification will be developed which will replace this specification and will define additional features that are necessary to support scenarios beyond SVG, such as integration into web browsers that support CSS. Once a general-purpose XBL is defined, sXBL would just become an SVG-specific subset (i.e., a profile) of the larger XBL specification.
Read the complete draft here.