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# expression Attribute

An XPath expression (relative to the expressionContext attribute, if specified) that must be evaluated to validate the XML Document Object Model (DOM) node specified in the match attribute.

## Type

    xsd:string

## Remarks

The expression attribute is a required attribute of the errorCondition element.

If the specified expression evaluates to True, it is considered to be an error condition and the specified error message is displayed.

## Example

The following is an example of the expression attribute as it is used in the errorCondition element:

    <xsf:customValidation>
       <xsf:errorCondition
          match="/exp:expenseReport"
          expressionContext="exp:reportDate"
          expression="msxsl:string-compare(., ../exp:startDate) < 0 and ../exp:startDate != """
          showErrorOn=".">
          <xsf:errorMessage
             type="modeless"
             shortMessage="The report date occurs before the end of the expense period.">
             The report date occurs before the end of the expense period. Verify that this is correct.
          </xsf:errorMessage>
       </xsf:errorCondition>
    </xsf:customValidation>

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