El XSD ya es probado con XML de ejemplo

.gitignore

@@ -0,0 +1 @@
+.yasd.py@*

README.md

@@ -1,3 +1,7 @@
+---
+WARN: It is just a prototype and currently just a subset of XSD capabilities.
+---
+
 # YASD, Yet Another Schema Definition
 
 YASD is a YAML format for human writable XSDs (XML Schema Definition), humans
@@ -22,7 +26,7 @@ flowchart LR
     sample --- |from| YASD3([YASD])
     YASD3 --> |to| XML([XML])
     document --- |from| YASD4([YASD])
-    YASD4 --> |to| MD([Markdown])
+    YASD4 --> |to| RST([reStructuredText])
     man --- |prints| README
 ```
 
@@ -32,11 +36,11 @@ To better understad what YASD does, see the inputs and outputs:
 
 -   Input: human workable schema in [YASD].
 -   Output: computer processable schema in [XSD].
--   Output: human readable documentation in [Markdown].
+-   Output: human readable documentation in [reStructuredText].
 
 ## Table of Contents
 
-[TOC]
+\[TOC\]
 
 ## Structure
 
@@ -47,7 +51,7 @@ To better understad what YASD does, see the inputs and outputs:
     elements:
       - ELMT
       ...
-    attributes:
+    attributeElements:
       - ATTR
       ...
     groups:
@@ -67,20 +71,19 @@ To better understad what YASD does, see the inputs and outputs:
     description: Element description
     type: simple|empty|no_text|no_elements|mixed 
     datatype: string|integer|decimal|date|time|language|duration|token|boolean|byte|int|double|float|long|short|normalizedString|dateTime|gDay|gMonth|gMonthDay|gYear|gYearMonth|negativeInteger|nonNegativeInteger|nonPositiveInteger|positiveInteger|unsignedLong|unsignedInt|unsignedShort|unsignedByte|anyURI|base64Binary|hexBinary|Name|QName|NCName|ID|IDREF|IDREFS|ENTITY|ENTITIES|NMTOKEN|NMTOKENS|NOTATION
-    default: a_value
-    fixed: a_value
-    restriction:
-      CONSTRAIN
-      ...
-    attribute:
-      - attribute_name
+    attributes:
+      - ref: attribute_name
+        use: optional|required|prohibited
+      - group: group_name
       ...
     children_order: all|choice|sequence
     children:
-      - name: element_name
-        maxOccurs: INTEGER
+      - ref: element_name
+        maxOccurs: INTEGER|unbounded
+        minOccurs: INTEGER
+      - group_ref: group_name
+        maxOccurs: INTEGER|unbounded
         minOccurs: INTEGER
-      - group: group_name
       ...
 
 ### Attribute (ATTR) structure
@@ -90,9 +93,8 @@ To better understad what YASD does, see the inputs and outputs:
     datatype: string|integer|decimal|date|time|language|duration|token|boolean|byte|int|double|float|long|short|normalizedString|dateTime|gDay|gMonth|gMonthDay|gYear|gYearMonth|negativeInteger|nonNegativeInteger|nonPositiveInteger|positiveInteger|unsignedLong|unsignedInt|unsignedShort|unsignedByte|anyURI|base64Binary|hexBinary|Name|QName|NCName|ID|IDREF|IDREFS|ENTITY|ENTITIES|NMTOKEN|NMTOKENS|NOTATION
     default: a_value
     fixed: a_value
-    use: required
     restriction:
-      CONSTRAIN
+      - CONSTRAIN
       ...
 
 ### Group (GRPS) structure
@@ -101,7 +103,7 @@ To better understad what YASD does, see the inputs and outputs:
     attribute_group: true|false
     children_order: all|choice|sequence 
     children:
-      - name: element_name
+      - ref: element_or_attribute_name
         maxOccurs: INTEGER|unbounded
         minOccurs: INTEGER
 
@@ -141,7 +143,7 @@ Mandatory.
 
 ### `name`
 
-Indicates element or attribute name.
+Indicates element, attribute or group name.
 
 Mandatory.
 
@@ -156,6 +158,12 @@ Naming rules:
     periods
 -   Element names cannot contain spaces
 
+### `ref`
+
+References element or attribute by name.
+
+Mandatory.
+
 ### `description`
 
 Indicates element or attribute description in human readable form.
@@ -172,21 +180,23 @@ Allowed types:
 
 -   `simple`. Only text node allowed.
 -   `empty`. Only attributes allowed.
--   `no_text`. No text nodes allowed.
+-   `no_text`. No children text nodes allowed.
 -   `no_elements`. No children elements allowed.
 -   `mixed`. Children elements, text node and attributes allowed.
 
 Chart:
 
-| type       | children elements | text node | attributes |
-|------------|:-----------------:|:---------:|:----------:|
-|simple      |          ✗        |      ✓    |       ✗    |
-|empty       |          ✗        |      ✗    |       ✓    |
-|no_text     |          ✓        |      ✗    |       ✓    |
-|no_elements |          ✗        |      ✓    |       ✓    |
-|mixed       |          ✓        |      ✓    |       ✓    |
+    | type        | elements | text | attributes |
+    |-------------|:--------:|:----:|:----------:|
+    | simple      | ✗        | ✓    | ✗          |
+    | empty       | ✗        | ✗    | ✓          |
+    | no_text     | ✓        | ✗    | ✓          |
+    | no_elements | ✗        | ✓    | ✓          |
+    | mixed       | ✓        | ✓    | ✓          |
 
-> **Note**: attributes are never mandatory; they could be zero or more.
+> **Note 1**: read "elements" and "text" with "direct children..." as prefix.
+
+> **Note 2**: attributes are never mandatory; they could be zero or more.
 
 ### `datatype`
 
@@ -264,27 +274,34 @@ Indicates default value when element or attribute is empty.
 
 Optional.
 
+Only allowed for simple elements or attributes.
+
 ### `fixed`
 
 Indicates fixed value to element or attribute.
 
-Optional.
+Optional; ignored if 'default' is present.
+
+Only allowed for simple elements or attributes.
 
 ### `use`
 
 Indicates that the attribute is required.
 
-Optional.
+Optional; if not present by default is `optional`.
 
-Only `required` is valid as value.
+Allowed uses:
+
+-   `optional`.
+-   `required`.
+-   `prohibited`.
 
 ### `restriction`
 
-Indicates accepted constrained values for element or attribute.
+Indicates accepted constrained values for attribute.
 
-Optional; if present, must contain at least one constrain.
-
-Not allowed for 'empty' and 'no_text' elements.
+Optional; if present, must contain at least one constrain and attribute
+`datatype` is ignored.
 
 Allowed constrains:
 
@@ -312,7 +329,7 @@ Allowed constrains:
     carriage returns) is handled; accepted values are
     `preserve|replace|collapse`.
 
-### `attribute`
+### `attributes`
 
 Indicates a list of attributes for an element.
 
@@ -353,7 +370,7 @@ Valid value is non negative integer.
 
 ### `group`
 
-Indicates group name.
+References group name.
 
 Optional.
 
@@ -380,9 +397,9 @@ Indicates elements for schema.
 
 Mandatory.
 
-### `attributes`
+### `attributeElements`
 
-Indicates attributes for schema.
+Indicates attributes elements for schema.
 
 Optional.
 
@@ -392,6 +409,15 @@ Indicates schema general information.
 
 Mandatory.
 
+## References
+
+-   "XML Schema Reference", [W3ref]
+-   "XML Schema Tutorial", [W3Schools].
+-   "XSD Tutorial", [Tutorials Point].
+
   [YASD]: https://gitlab.com/amlengua/apal/esquema/-/blob/main/apal.yaml
   [XSD]: https://gitlab.com/amlengua/apal/esquema/-/blob/main/apal.xsd
-  [Markdown]: https://gitlab.com/amlengua/apal/esquema/-/blob/main/apal.md
+  [reStructuredText]: https://gitlab.com/amlengua/apal/esquema/-/blob/main/apal.rst
+  [W3ref]: https://www.w3schools.com/xml/schema_elements_ref.asp
+  [W3Schools]: https://www.w3schools.com/xml/schema_intro.asp
+  [Tutorials Point]: https://www.tutorialspoint.com/xsd/