IS-SDF-STRUCTURE( ) Analyze string against criteria for SDF structures

The IS-SDF-STRUCTURE( ) function analyzes whether the specified string is an SDF structure.

The specified SDF structure must be introduced by a value. This value must not be omitted, or else the string will be regarded as an SDF list and not as an SDF structure.

Result type: BOOLEAN

IS-SDF-STRUCTURE( )

STRING = string_expression