# OpenLink Virtuoso Universal Server: Documentation - ForcedCalculateableValue

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Virtuoso Functions Guide

## ForcedCalculateableValue

The type of attribute that contains an expression to be calculated at run time.
Description

The type of an expression. The value of this type must be started with '--', the rest of string is the text of an expression to be calculated in order to get the effective value of the property.

The type identifier 'ForcedCalculateableValue' is introduced only for diagnostic purposes, you will never use it in VSPX code. When Virtuoso server tries to compile an invalid VSPX page, you might see a diagnostic messages like 'the value of attribute X of a control Y does not match pattern ... for type ForcedCalculateableValue'. If you see this then you should check the syntax of the value of the specified attribute.