Constant CLASS_DOCS_ONLY_MARKER 

pub(crate) const CLASS_DOCS_ONLY_MARKER: &str = ".__MX_CLASS_DOCS_ONLY__";

Opens a class’s roxygen block that only carries the impl docs (docs_only_class_block). The wrapper writer writes the block, up to its closing NULL, only when the type’s impl docs or member-derived class docs say something, so a readers-only impl adds no page (#1918). Spelled the same as miniextendr_api::registry::CLASS_DOCS_ONLY_MARKER.