Copyright (c) 2019-2024 Sempare Limited
Stack frames are created when a template is being evaluated. This will contain the _ value.
'if', 'for', 'with' and 'while' statements also define stack frames to contain variables defined within their scope.
When a template is being processed, a root stack frame is created. All variables in the context are added to this stack frame.
When you provide an input variable to Template.Eval(), the _ variable is also set.