The Complete Story

To summarize the use of numbering information in a document, the paragraph properties specify a <numPr> element, which references a numbering definition instance via the <numId> element. The numbering definition instance specifies an inherited abstract numbering definition via the <abstractNumId> element. The paragraph then also specifies the list level from the numbering definition instance using the <ilvl> element.

Consider the following WordprocessingML for a numbered paragraph:

<w:p>
  <w:pPr>
    <w:numPr>
      <w:ilvl w:val="0" />
      <w:numId w:val="5" />
    </w:numPr>
  </w:pPr>
  <w:r>
    <w:t>Numbered paragraph</w:t>
  </w:r>
</w:p>

Based on the <numId> of 5, the paragraph uses the numbering definition instance with a @numId of 5:

<w:numbering>
  ...
  <w:num w:numId="5">
    <w:abstractNumId w:val="4" /> 
  </w:num>
</w:numbering>

Based on the <abstractNumId> of 4, this instance inherits the abstract numbering definition with an @abstractNumId of 4:

<w:numbering>
  <w:abstractNum w:abstractNumId="4">
    <w:nsid w:val="FFFFFF7F" />
    <w:multiLevelType w:val="singleLevel" />
    <w:lvl w:ilvl="0">
      <w:start w:val="1" />
      <w:lvlText w:val="%1." />
      <w:lvlJc w:val="left" />
      <w:pPr>
        <w:tabs>
          <w:tab w:val="num" w:pos="720" />
        </w:tabs>
        <w:ind w:left="720" w:hanging="360" />
      </w:pPr>
    </w:lvl>
  </w:abstractNum>
  …
</w:numbering>

Since the numbering definition instance does not specify an override for @ilvl 0, the definition for the corresponding level from the abstract numbering definition is applied to the text.