Out-Of-Box Door Opening Family - Opening Mask?

[rloVW7ZH]

Hi all,

I'm hoping for some clarification with something pretty basic.
Pardon of if this is a bit long winded. Hoping the context will give you more information to make me some recommendations.

I am in Structural.
Depending on the project, we will have a combination of opening types (door, window, and wall opening).

Depending on the project, we may copy elements from the arch model, (walls, floors, doors and windows) then swap to matching type using our naming, and materials.
For the doors and windows, we use a stripped down family with just the opening.

The door and window families we use are slightly tweaked versions of:
"Door-Opening.rfa"
"Window-Square Opening.rfa"

I'm looking at that out-of-box "Door-Opening.rfa",

I'm trying to figure out why there is a detail item, "Opening-Mask".
Editing that family, the lines are set to Subcategory "Overhead".

Can you help enlighten me on the intended purpose of this masking region?
And when these "Overhead" lines are meant to be seen?

Sorry if this is a bit of a basic question.

But some things arch discipline might use daily, I'm trying to understand what the proper usage is so I can apply it to Struct.

Thank you so much!

[Simon_Weel · Accepted solution]

The Overhead lines should show up in a plan view to indicate there's a wall above the opening. Not sure why there's a masking region? Anyway, it's an aesthetic thing.