The Bind Module

2.1 The bind Element

The bind element uses a node-Set Binding to assign Model Item Properties to the selected instance data nodes. If the bind element has an attribute of type xsd:ID, then it also associates the specified identifier with the instance data nodes the bind selects.

Common Attributes: Common , Node-Set Binding, Model Item Properties

2.2 The bind attribute

The bind attribute is added to the Node-Set Binding and Single-Node Binding attributes set. The bind attribute will contain an IDREF to a bind element, which will provide the node-set for the binding. For a Single-Node Binding the first node rule is applied.

When a bind attribute is encountered on a bind element the bind element and all it's descendant binds are ignored.

It is an exception (xforms-idref-exception) if the XForms Processor encounters a bind attribute IDREF value that refers to an ID that is not on a bind element.

2.3 The mip Element

The mip element adds support for attaching custom Model Item Properties to data nodes.

Special Attributes:

name

Required. Name of the Model Item Property.

value

Optional. An XPath expression to be evaluated. The result should be convertible to to the type specified by the type attribute.

The conversion is done using the XPath functions string(), boolean() and number() for the types xs:string, xs:boolean and xs:number respectively.

type

Optional The type of the value of the Model Item Property. The type attribute supports values xs:string, xs:boolean and xs:number. The default value is "xs:string".

cascade

Optional If the cascade property is "true" the Model Item Property will also be applied to all the descendants of the data node to which this Model Item Property applies. The default value is "false".

combine-cascade

Optional An XPath expression that specifies how the local and cascaded value of a Model Item Property should be combined. The result should be convertible to to the type specified by the type attribute. The default value is "error('xforms-binding-exception')".

The local and cascaded value are made available to the XPath expression through XPath variables $local-value and $cascaded-value respectively.

<bind nodeset="//total">
  <mip name="readonly" value="true()" type="xs:boolean" cascade="true" combine-cascade="$local-value or $cascaded-value"/>
</ bind>

2.4 Model Item Properties Attribute Collection

Model item properties are infoset contributions made to instance data nodes and can be distinguished along various axes.

Computed expressions vs. fixed properties:

• Fixed properties are static values that the XForms Processor evaluates only once. Such properties consist of literals, and are not subject to XPath evaluation.

• Computed expressions are XPath expressions that provide a value to the XForms Processor. Such values are recalculated at certain times as specified by the model which they are defined. These expressions encode dynamic properties, often constraints, such as the dependency among various data items. Computed expressions are not restricted to examining the value of the instance data node to which they apply. XPath expressions provide the means to traverse the instance data; more complex computations may be encoded as call-outs to external scripts.

Inheritance rules:

Some model item properties define inheritance rules, in which case the XForms Processor needs to keep track of two separate values: 1) the local value, which is applied from an attribute of element bind, and 2) the inherited value, which is determined by combining the evaluated local value with the evaluated values from ancestor nodes in the instance data.

Assigning local values:

Local values are assigned by processing all bind elements in an XForms Model in document order. It is an error to attempt to set the same model item property twice on the same node.

2.5 Evaluation Context

The evaluation context of a Model Item Property expression of a bind element is the in-scope evaluation context. But the Model Item Properties are attaches to the nodes of a nodeset binding if the bind element specifies a nodeset binding, and otherwise the bind element attaches the Model Item Properties to the initial in-scope evaluation context.

2.6 Rebuild action

2.7 Error Indications

Error indications happen as a result of unusual conditions in the XForms Processor. This module contains only "fatal" errors, which halt processing, and bear the suffix "exception". For all events in this section, it is permissible for the XForms Processor to perform some kind of default handling, for example logging error messages to a file.