Field numbers
Captions and LISTNUM fields are examples of field-based numbering.
In captions, the field is a simple SEQ field. A SEQ field can belong to only one sequence and it can produce only one level of numbering. You can make heading numbering using SEQ fields: if you do, you have to define a named sequence for each level of numbering. You also need to handle your own re-setting of each level when a higher level occurs.
The SEQ field takes a "name" that identifies which list contains this particular SEQ field. For captions, that name must be "Caption." When SEQ fields go wrong, it's usually because you have forgotten to update them, or the list name is wrong. To update SEQ fields, select all the document text (Ctrl + a) and hit F9.
LISTNUM fields are a much more advanced kind of field introduced in Word 97. They are a bit flighty, because Word maintains and automatically updates them. And there is a bug in the Help: it appears as though you can define various list names in a LISTNUM field the same way as you can in SEQ fields. In fact, you can't: there are only three pre-defined list names: AUTONUM, AUTONUMOUT, and AUTONUMLGL. It also appears that you can control the formatting of a LISTNUM using switches: again: wrong! The name in the list name parameter controls the numbering formatting. Each of the three names has predefined formatting: what you see is what you get.
The LISTNUM field is a single field that generates nine levels of numbering. It reads the "level" property of the paragraph format to determine which level to display. You can have multiple LISTNUM fields within a paragraph: if you have, they number sequentially from the beginning of the paragraph. You can have multiple levels of LISTNUM field in a paragraph: if you select the LISTNUM field result and press the Indent or Outdent buttons, the level will change, overriding the level of the paragraph. This is the first place to look if a LISTNUM field won't behave: once set, the hard-coded level set in the LISTNUM field does not change if you change the level of the containing paragraph. Reveal field codes and remove the level parameter to make it behave.
Technical writers often use AUTONUMLGL fields to generate heading numbering. They are rock-solid stable and transportable across all versions of Word from Word 6 to Word 2000. Microsoft makes concerted attempts in the Help to steer us away from these fields: instead suggesting that we should use Outline Numbered Lists or LISTNUM fields. Sorry, we're not that silly! LISTNUM fields are not backwards compatible with Word versions earlier than Word 97. Most other word-processors haven't a clue what to do with LISTNUM fields. Everything can handle AUTONUMLGL fields. Moreover, if Outline List Numbering was any good, you wouldn't be reading all this!