Early books using syntax diagrams include the "Pascal User Manual" written by Niklaus Wirth[1] (diagrams start at page 47) and the Burroughs CANDE Manual.
[2] In the compilation field, textual representations like BNF or its variants are usually preferred.
Railroad diagrams are visual, and may be more readily understood by laypeople, sometimes incorporated into graphic design.
The canonical source defining the JSON data interchange format provides yet another example of a popular modern usage of these diagrams.
Red (programming language) Parse Dialect: This format also supports ranges, e.g. digit: charset [#"0" - #"9"], but it is not used here for consistency with the other examples.