One field controls the contents of others?

[Geoff Hart <Geoff-h -at- MTL -dot- FERIC -dot- CA>]

Chris Tolliver wondered how to <<...document a dialog box
where your selection for the main field... determines what
other fields are available? ... On the Trust Information dialog
box, the... main field is a drop-down box titled "Trust Type."
For Trust Type, you can select: Grantor Retained Trust,
Charitable Remainder Trust, or Qualified Personal Retained
Trust. The remaining contents of the dialog box change,
depending on what you select.>>

In this case, you should let the way the user interacts with the
interface to achieve their goals guide your choice of design:
the more closely your documentation follows the user's
typical path, the more useful it will be to the user.

Based on your description, I'd document this as follows: a
main task-based heading entitled "Picking a type of trust",
followed by a very short introductory paragraph that
introduces the types of trust available to users (since these
three types aren't visible on the screen until the user clicks the
button, you need to alert users to their existence), then three
subheadings (one per trust). So the result would be something
like this:

****************************************
Choosing a type of trust
----------------------------

To choose one of the available types of trust, click the Trust
Type button. The drop-down menu that appears lets you
select one of the following options:
- Grantor Retained Trust
- Charitable Remainder Trust
- Qualified Personal Retained Trust

Depending on which you choose, your options in the
remainder of the screen will change. The following sections
describe the characteristics of each trust type and the
available options that the software displays when you choose
that trust type.
[three subheadings, each followed by a brief explanation of
the trust and listing of the options]
******************************************

This is easy to maintain, because you haven't explicitly
named the number of options, so you can simply extend the
bulleted list as necessary. It also translates well into online
format because each bullet can become a hyperlink to the
appropriate section of the manual.

--Geoff Hart @8^{)}     Pointe-Claire, Quebec
geoff-h -at- mtl -dot- feric -dot- ca

"Though the editor is the author's ally, she should never forget that
she is also the reader's first line of defense."--Shoshanna Green

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