We can trace this behavior to the property definition file "form.json" - https://github.com/jogetworkflow/jw-community/blob/6.0-SNAPSHOT/wflow-core/src/main/resources/properties/form/form.json#L81
This is the excerpt of the file that is responsible to generate such dropdown selection.
{
name: 'postProcessor',
label:'@@form.form.postProcessor@@',
type:'elementselect',
options_ajax:'[CONTEXT_PATH]/web/property/json/getElements?classname=org.joget.plugin.base.ApplicationPlugin',
url:'[CONTEXT_PATH]/web/property/json[APP_PATH]/getPropertyOptions',
default_property_values_url: '[CONTEXT_PATH]/web/property/json[APP_PATH]/getDefaultProperties'
}
Explanations on the code above
Line 4 - Attribute "type" with the value set to "elementselect" is important to tell the property editor on how to handle the selection. A new tab will be created automatically upon a selection made.
Line 5 - Attribute "options_ajax" with the service URL set is responsible to load all the plugin tied to "org.joget.plugin.base.ApplicationPlugin" (Process Tool) into the selection. You may change the value to load the appropriate type of plugin you want.
[CONTEXT_PATH] is a special variable that will be replaced automatically at runtime with the Joget web app context information. (e.g. http://localhost:8080/jw)
Line 6 - With the value in Line 4 set, the property editor will make a call to this URL, passing along the selection made. (e.g. http://localhost:8080/jw/web/property/json/expenseclaim/1/getPropertyOptions?value=org.joget.apps.app.lib.EmailTool)
[CONTEXT_PATH] is a special variable that will be replaced automatically at runtime with the Joget webapp context information. (e.g. http://localhost:8080/jw)
[APP_PATH] is a special variable that will be replaced automatically at runtime with the Joget App context information. (e.g. /expenseclaim/1)