We introduced tilde syntax in early 2017 and documented this change in both the release notes and our documentation.
The documentation you are referencing is new to our help portal but the change is not new. You can also see a discussion on the new email editor thread where we guided users in February 2018 on how to create blind form submits using the new editor here: Eloqua Product Update: Our New (Responsive) Email Design Editor Arrived with 18A (Feb 2018).
Sorry that you ran into that issue. Let me know if you need help understanding the tilde syntax format.
Oracle Eloqua Product Managment