tighterror: add Variant Types documentation

src/lib.rs

@@ -240,7 +240,28 @@
 //!   errors in the category, or in [module object](#module-doc-from-display)
 //!   to affect all errors in the module.
 //!   Values defined on lower levels win.<br>
-//!   Default: `false`<br>
+//!   Default: `false`<br><br>
+//!
+//! * `variant_type` - bool|string (optional)<a name="err-obj-variant-type"></a>
+//!
+//!   Enables creation of a Variant Type for this error.
+//!
+//!   When specified as a boolean `true|false` it enables/disables creation
+//!   of a Variant Type for this error. When enabled the name of the Variant
+//!   Type is derived by converting the error name case from UPPER_SNAKE to
+//!   UpperCamel, e.g., `OPERATION_TIMEOUT` becomes `OperationTimeout`.
+//!
+//!   To customize the Variant Type name it is possible to specify this
+//!   attribute as a string. In this case the value of the attribute becomes
+//!   the name of the Variant Type. It must be a valid Rust struct name
+//!   specified in UpperCamel case.
+//!
+//!   This attribute can be enabled on a higher level in
+//!   [category object](#category-variant-type) or in
+//!   [module object](#module-variant-type).
+//!   Values defined on lower levels win.
+//!
+//!   Default: `false`<br><br>
 //!
 //! ### Error Object Examples
 //!
@@ -434,6 +455,18 @@
 //!   (see below) this attribute is forbidden, and the error list must be
 //!   defined as a root-level attribute.<br><br>
 //!
+//! * `variant_type` - bool (optional)<a name="category-variant-type"></a>
+//!
+//!   Sets a default value for the [`variant_type`](#err-obj-variant-type)
+//!   *error object* attribute. This affects errors belonging to this category
+//!   only. The value is used for all errors that do not define this property
+//!   explicitly as part of *error object* specification.
+//!
+//!   Customization of Variant Type name is possible only in the *error object*
+//!   specification.
+//!
+//!   Default: `false`<br><br>
+//!
 //! ### Category Object Examples
 //!
 //! A specification with a single implicit category `General`. Note, the error
@@ -753,6 +786,20 @@
 //!    to create a `Result<T, Error>` from `ErrorKind`.<br>
 //!    Default: `true`<br><br>
 //!
+//! * `variant_type` - bool (optional)<a name="module-variant-type"></a>
+//!
+//!   Sets a default value for the [`variant_type`](#err-obj-variant-type)
+//!   *error object* attribute. This affects errors belonging to all categories
+//!   in this module. The value is used for all categories and errors that do
+//!   not define this property explicitly as part of
+//!   [category object](#category-variant-type) or
+//!   [error object](#err-obj-variant-type) specification.
+//!
+//!   Customization of Variant Type name is possible only in the *error object*
+//!   specification.
+//!
+//!   Default: `false`<br><br>
+//!
 //! ### Module Object Examples
 //!
 //! YAML