ORA-XQ-216-E: Explanation of initial /, // and non-initial / and // as path separators in abreviation

SECTION 3.2.4: Abbreviated Syntax

3.2.4, bullet 3, gives an explanation of // as
being effectively replaced by /descendant-or-self::node()/

However, this is only true for // used in non-initial positions.
If // is used at the beginning of a path expression, it is 
effectively replaced by 
fn:root(self:node()) treat as document-node()/descendant-or-self::node()
as explained in 3.2 Path Expressions.

So we need to make it clear here. Or repeat the abbreviation of
the initial '/' and '//'  here in 3.2.4 as well.

- Steve B.