I agree it's not easy to Google for the Declarative Pipeline or Groovy Sandbox. Here's the comparison of the two syntaxes available in Jenkins Pipeline (Scripted and Declarative):
Here are details on the Groovy Sandbox (provided by the Script Security Plugin and installed by default when installing recent Jenkins). The Groovy Sandbox is on by default for Jenkins Pipeline:
Seriously? Downvotes? On a holiday on a plane and I get down votes asking for a little help? I did try and google and didn't find the stuff.