Structure of docx field

A field in docx is represented this way.

  <w:r>
    <w:fldChar w:fldCharType="begin"/>
  </w:r>
  AAA
  <w:r>
    <w:instrText xml:space="preserve"> NOTEREF _Ref111111 \h </w:instrText>
  </w:r>
  BBB
  <w:r>
    <w:fldChar w:fldCharType="separate"/开发者_如何转开发>
  </w:r>
  CONTENT
  <w:r>
    <w:fldChar w:fldCharType="end"/>
  </w:r>

The field content goes to the CONTENT placeholder. My question is: can anything go to AAA or BBB? Or they are always empty? I suspect the creators of this format had something in mind to have four separator elements instead of just two, but I haven't seen any examples of using this.

It's better to think of it as only three separator elements and two slots for content, which can be complex thanks to the separators.

  <w:r><w:fldChar w:fldCharType="begin"/></w:r>
  LABEL
  <w:r><w:fldChar w:fldCharType="separate"/></w:r>
  VALUE
  <w:r><w:fldChar w:fldCharType="end"/></w:r>

So your AAA and BBB are just extra content for the LABEL.

There's an example in the spec, where LABEL is:

<w:r><w:rPr><w:b/><w:color w:val="ED1C24"/><w:u w:val="single"/></w:rPr>
     <w:instrText>D</w:instrText></w:r>
<w:r><w:instrText xml:space="preserve">ATE</w:instrText></w:r>

to make the D in DATE a different style.