form.json

{
	"fieldSets": [{
		"fields": [
			{
				"dataType": "string",
				"defaultValue": "custom",
				"description": "src",
				"label": "src",
				"name": "src",
				"type": "select",
				"typeOptions": {
					"validValues": [
						{
							"label": "demo",
							"value": "{'default': 'https://go.pardot.com/l/854303/2020-04-16/84zs','es_ES': 'https://go.pardot.com/l/854303/2020-05-20/czgy'}"
						},
						{
							"label": "download",
							"value": "{'default': 'https://go.pardot.com/l/854303/2020-04-20/8ctl'}"
						},
						{
							"label": "custom",
							"value": "custom"
						}
					]
				}
			},
			{
				"dataType": "string",
				"description": "custom-src",
				"label": "custom-src",
				"name": "customSrc",
				"type": "text"
			}
		]
	}]
}