Originally proposed by Niklaus Wirth in 1977 as an alternative to Backus–Naur form (BNF).
[2] It was also used to define the syntax of EXPRESS, the data modelling language of STEP.
Wirth later incorporated some of the concepts (with a different syntax and notation) into extended Backus–Naur form.
One of the problems with BNF which this example illustrates is that by allowing both single-quote and double-quote characters to be used for a literal, there is an added potential for human error in attempting to create a machine-readable syntax.
One of the concepts that migrated to later meta syntaxes was the idea that giving the user multiple choices made it harder to write parsers for grammars defined by the syntax, so computer languages in general have become more restrictive in how a quoted-literal is defined.