Features used to implement the example

• Boolean validator with math, date-time or text-string terms

Example: Validate compatible values selection among dependent custom fields

I have three pull-down 

• PD1 = (element11, element12, element13)
• PD2 = (element21, element22, element23)
• PD3 = (element31, element32, element33)

Logic goes like

• If (PD1.element11) is selected display PD2 & PD3
• If (PD1.element12) is selected display PD2, disable PD3
• If (PD1.element13) show or disable PD2 & PD3

With Jira Workflow Toolbox you can implement a validation in a transition (also at "Create Issue" transition) indicating incompatible value selection for fields PD1, PD2 and PD3. To do it you can use Boolean validator with math, date-time or text-string terms with the following configuration:

Text to be parsed is: (%{11800} != "element12" OR %{11801} != null AND %{11802} = null) AND (%{11800} != "element13" OR %{11801} = null AND %{11802} != null)

Note that field codes in the particular instance of Jira used for this example are:

• %{11800} is field code for custom field "PD1"

Once configured, transition "Create Issue" will look like this: