Which parameters an operation can use

Any parameter the element has: shared, project, family parameters (shared or not) and Revit's own built-in ones. Every parameter field works the same way.

A parameter field: the built-in parameter Mark picked as a chip, its locked Instance tag and the database button

Two ways to name a parameter

Type the name exactly as the Properties palette shows it. When the operation runs, FlexiData looks for a parameter of that name on each element — or on its type, see below — whatever kind of parameter it is. Suggestions come from the Dictionary.
Or pick a built-in parameter with the database button at the end of the field — see Built-in parameters. A picked one is found by its identifier, in a Revit of any language; a built-in typed by name is found only in a Revit that calls it that (Mark in English, Kennzeichen in German) — see Languages.

Kind of parameter	How to name it
Shared parameter	Type its name
Project parameter	Type its name
Family parameter, shared or not	Type its name
Built-in parameter (Mark, Comments, Fire Rating…)	Pick it from the list — or type the name your Revit shows

Instance or type

The tag inside the field says Instance (the parameter is on the element itself) or Type (on its type). Click it to switch a typed parameter. A picked built-in shows a lock: Revit decides. When a type is written from values of its instances, see Instance and type parameters.

Good to know

Warning

If an element has two parameters of the same name — a shared and a family parameter, say — the first one Revit finds is used. Keep names unique.

Global parameters belong to the project, not to elements, and cannot be used.
A parameter must exist on the elements — FlexiData fills parameters, it does not create them. A name that matches nothing is named by the Executor's configuration check before the run.
A read-only parameter — one Revit computes, such as Area or Volume — can be read but not written; the report lists such elements.