provides a parameter for a model behaviour by supplying its name and an XPath expression identifying the location of its content. a name for the parameter being supplied. when used with behaviour alternate, a parameter of this name supplies one of the pair of possible values; for example the regularized form rather than the original form within a choice element. when used with behaviour alternate, a parameter of this name supplies one of the pair of possible values; for example the original form rather than the regularized form within a choice element. when used with behaviour graphic, a parameter of this name supplies a value for the height of the graphic e.g. 300px, 50%. a parameter of this name should supply a unique identifier for the element being processed; as for example with the anchor behaviour a parameter of this name should supply an expression to be used to label something, for example concat('Page ', @n) for a page beginning or @n for a footnote reference; typically used with the note or break behaviours when used with the heading behaviour, a parameter of this name supplies a positive integer indicating the hierarchic level of a heading. when used with the link behaviour, a parameter of this name should supply a URL to be used as the target of a link. when used with the note behaviour, a parameter of this name should provide a string which describes the intended placement of some text; typical values include margin, footnote, endnote, inline, bottom a parameter of this name can be used to categorize the specified behaviour in any way; for example the kind of break (when used with the break behaviour) or the kind of index to be generated (if used with the index behaviour) etc. when used with behaviour graphic, a parameter of this name supplies a a URL indicating the graphic intended. when used with behaviour graphic, a parameter of this name supplies a value for the width of the graphic e.g. 400px, 70%. supplies an XPath expression which when evaluated provides the value for the parameter

In this example, which will be processed for a choice element which has both sic and corr child elements, the default parameter will provide the value of the child corr element, and the alternate parameter will provide that of the child sic elements. If neither param element was supplied, both elements would still be available to an application, but the application would need to distinguish them for itself.

An implementation may require parameters other than those listed here, and is not required to follow this partial specification.

The names and datatypes of the expected parameters should be documented in the corresponding customization using a paramSpec element. Literal strings provided in an XPath expression should be quoted.