Constant EXPLAIN 

pub const EXPLAIN: &str = "Explain a graph node: its record and its provenance-labelled incoming/outgoing edges. Keys \
    look like `sym:<lang>:<path>#<Name>`, `file:<path>`, `adr:<id>`. A key may be \
    project-qualified (`<project>::<key>`) to follow a cross-repo link into another hosted \
    project (see `list_projects`).";

explain.