Template parameters indicate values for controlling content in documents based on a template. You can use template parameters with optional regions or editable tag attributes, or to set values you want to pass to an attached document. For each parameter, you select a name, a data type, and a default value. Each parameter must have a unique name; each name is case sensitive.
Template parameters are passed to the document as instance parameters. In most cases, a template user can edit the parameters default value to customize what appears in a template-based document. In other cases, the template author might determine what appears in the document, based on the value of a template expression (see Template expressions).