Data Format Description Language (DFDL) v1.0 Specification
OGF Proposed Recommendation GFD-P-R.174, January 31, 2011


23.3 General Syntax

DFDL expressions follow the XPath 2.0 syntax rules but are always enclosed in curly braces “{“ and “”.

When expressions are used for a property which accepts a string literal then “{{“should be used to escape when a “{“is required as a character.

Examples
{/book/title }
{$x+2 }
{if (fn:exists(../field1))  then 1 else 0  }   

The result of evaluating the expression must be a single atomic value of the type expected by the context. Expressions must not return a sequence containing more than one item or a processing error will occur. If the expression returns an empty sequence it will be treated as returning nil.


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