Working with conditional paragraph styles
A conditional paragraph style is another way of formatting text differently in different parts of your document. In some cases, you may find it saves time to use conditional styles rather than switching between styles as you type.
Making a paragraph style conditional means it changes its formatting depending on where it is used. For example, you may want the style MyTextBody to be black by default but turn white when inside a frame with a blue background.
Probably the most common use for conditional formatting is with single style outlining. Single-style outlining is a type of outline numbering designed with a Numbering style, rather than with Tools > Outline Numbering. Instead of using different styles, it changes the number formatting whenever you press the Tab key to create a subordinate heading.
The only trouble with single-style outlining is that all levels look the same. That is where a conditional paragraph style comes in handy. Assign the paragraph style to an outline numbering style in the Numbering page and then open the Condition page (Figure 214). There, you can assign the levels of the outline numbering style to other paragraph styles. Then, when you press the Tab key while using the paragraph style, each level of the outline takes on different formatting, making single-style outlining even more convenient than it is on its own.
Predefined styles (other than Text Body) such as Default, Heading 1, and Heading 2 cannot be set to be conditional.
If you want to make a style conditional, you have to do it while the style window still is open for the first time. After the window closes, the Condition tab no longer appears in the window.