ODF 1.0 and ODF 1.2 did contain the schema in Relax-NG XML syntax. Using RNG Compact as suggested would be equivalent, except that the notation would be more compact.

Including the schema into the specification, regardless which syntax is used, has the disadvantage that the specification structure has to follow the structure of the schema, which is not always appropriate. For that reason, the schema is not embedded in the specification any longer in ODF 1.2, but available as a separate document.

The paragraphs with the orange background color have been added to provide cross references between the elements and attributes. They are informative, and are not an attempt to repeat what is said formally in the schema in by natural language.

What is missing in indeed missing is an explanatory sentence in the notation section of the specification. Further, the formatting of the informative paragraphs should be changed.

Suggestion:

The informative element and attribute lists may get a border. The background color may be change to a 10% gray, or even transparent.

In section 1.6 Notation, we may add:

Text with a gray background color which is contained in boxes is informative. It lists the element-element and element-attribute relations for cross reference purposes.

Correction will appear in OpenDocument-v1.2-part-1-cd03-rev03.

For part 3, I've inserted an "XML" in the 2nd sentence. The full section "Notation", which is now called "Terminology", reads as follows:

All text is normative unless otherwise labeled.
Text with a gray background color which is contained in boxes is informative. It lists the XML element-element and element-attribute relations for cross reference purposes.
Within the normative text of this specification, the terms "shall", "shall not", "should", "should not", "may" and "need not" are to be interpreted as described in Annex H of [ISO/IEC Directives].
XML Element and attribute names as well as attribute value types and values appear in a monospace font.