reorganize module

_archive/rhai_engine/rhaibook/engine/metadata/index.md

@@ -0,0 +1,49 @@
+Functions and Custom Types Metadata
+===================================
+
+{{#include ../../links.md}}
+
+~~~admonish warning.small "Requires `metadata`"
+
+Exporting metadata requires the [`metadata`] feature.
+~~~
+
+
+Functions
+---------
+
+The _metadata_ of a [function] means all relevant information related to a function's
+definition including:
+
+1. Its callable name
+
+2. Its access mode (public or [private][`private`])
+
+3. Its parameter names and types (if any)
+
+4. Its return value and type (if any)
+
+5. Its nature (i.e. native Rust or Rhai-scripted)
+
+6. Its [namespace][function namespace] ([module] or global)
+
+7. Its purpose, in the form of [doc-comments]
+
+8. Usage notes, warnings, examples etc., in the form of [doc-comments]
+
+A function's _signature_ encapsulates the first four pieces of information in a single concise line
+of definition:
+
+> `[private]` _name_ `(`_param 1_`:`_type 1_`,` _param 2_`:`_type 2_`,` ... `,` _param n_`:`_type n_`) ->` _return type_
+
+
+Custom Types
+------------
+
+The _metadata_ of a [custom type] include:
+
+1. Its full Rust type name
+
+2. Its pretty-print _display name_ (which can be the same as its Rust type name)
+
+3. Its purpose, in the form of [doc-comments]