3.1 b-h: LABEL attributes

 Dimension 1: Which pieces of information should be specified for
 possible inclusion in linking elements?
 e. caption
ERB consensus:
 - we will refer to this as a Label, not an explainer or caption
 - there is strong support for having labels.  

However, the ERB is unhappy with allowing only a simple character string; 
how does one support multilingual labeling, or labels which are graphic?  
Our provisional solution is to support both a RESOURCE LABEL attribute and/or 
a RESOURCE LABEL LOCATOR attribute, the latter being used to locate and
retrieve a structured label.  But then do we need a LABEL LOCATOR
SCHEME?  Or make it use the same scheme as the resource locator?  We
decided to defer this until we had a better understanding of linktypes and