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Users can configure regular expressions (to force the selection of certain parameter values for certain users) and visibility expressions (to hide the parameter based on the visibility expression's result) for parameters to customize the Start Workflow form in Portal:
Regular Expressions
A regular expression (shortened as regex) is a sequence of characters that define a search pattern. This pattern is used in Start Workflow form for input validation to allow/prevent the execution of a workflow. If the input validation matches the regex pattern, the execution can be started, otherwise the execution of the workflow is prevented until the input value matches the regex pattern. The regex message can be customized for a better understanding of the values expected in Start Workflow form:
In order to test the regex, input a Test Value and click on 
. An Info window will open stating if the regex test passed or failed:
In order to save the configuration, click on Save button before switching to another parameter.
Visibility Expressions
Enable Custom GUI
The user can configure the Custom GUI by clicking Enable Custom GUI and Custom GUI.
The visibility expression determines if the parameter it is applied on, will be visible or not in Start Workflow form. If the expression will evaluate to True, then the parameter will be visible otherwise not. Type a visibility expression in the field. If help regarding the expression construction is needed you can click the ? button. Here are some helpful examples:
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