In [Summary of structural containers](https://docs.asciidoctor.org/asciidoc/latest/blocks/delimited/#summary-of-structural-containers), the spec shows the initial (typically four) characters of the delimited block (i.e. `====` for an example block). In the subsequent section [Nesting blocks](https://docs.asciidoctor.org/asciidoc/latest/blocks/delimited/#nesting), it says: > When nesting a delimited block that uses the same structural container, it’s necessary to vary the length of the delimiter lines … It does not say whether the extra characters used to alter the length can be arbitrary or must match the last specified character. In other words, would `====xyz` be valid as an example block delimiter or only `====` plus any number of `=` characters? My current working assumption (I'm writing an [AsciiDoc parser in pure Rust](https://github.com/scouten/asciidoc-parser)) is that the extra characters must match the last character specified in the delimiter.