The elementary checks precede use of the validator table (as described in relation to the validatorDataTable property), and all checks precede use of the validatorFunction property. This order of events is important because the validator function can do cross-field checking, and such checking often requires valid field values.
The value of validatorFunction is a validator function that you write. You code that function with no parameters and such that, if the function detects an error, it requests the re-display of the form by invoking ConverseLib.validationFailed.
If validation fails when you specify one of the two system functions, the displayed message is based on the value of the property validatorFunctionMsgKey. If validation fails when you specify a validator function of your own, however, the function does not use validatorFunctionMsgKey, but displays a message by invoking ConverseLib.validationFailed.
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Text forms