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Float-like thing in clutch master cylinder tank?

Does anybody know the purpose of a black float-like thing in the clutch master cylinder fluid tank? It’s not attached to anything, just seems to float on top of the fluid. I didn’t re-install it when I replaced the clutch master cylinder. It seemed to be degrading and releasing gunk into the fluid. The replacement MC didn’t have one of those included. It’s loss seems to have no effect on the clutch performance. Any ideas what it is for?

Sorry for the complete guess, but my guess would be that it took up volume so the original factory unit wouldnt require as much fluid to fill

It is, in fact, a float, but I’d be lying if I didn’t admit ignorance to its purpose.
So I’m going to guess that if the fluid level gets too low it seals the port from the reservoir to the master cylinder chamber to prevent air from being drawn in.

You may well be right about that TSM. However, if the fluid got that low, some problem needing att’n is happening, and bleeding the line will probably be necessary anyway. Plus it is a simple thing to bleed. I was thinking it might be to prevent fluid from splashing up during aggressive clutch pedal maneuvers. I don’t know why splashing would be bad though. Maybe it could create air pockets.

Perhaps it attenuates pressure spikes? Perhaps it seals the reservoir vent hole if a fluid surge fills the reservoir?
I have to admit, this one has piqued my curiosity. In looking at an MC design, I cannot determine for certain its actual purpose. I think I’ll haul out an old textbook and see if I can find a reason for its existence. If I do, I’ll post.

Found it. It acts as a diaphragm to prevent the absorption of moisture by the fluid.
Duh!!! I’m SO embarrassed!!!

Interesting. It blocks the surface of the fluid from water-vapor-containing ambient air. I can see that might do some good. Thanks TSM for taking the time to look it up and post. Since the new CSM I installed didn’t have one included, & the original is degraded, nothing on RockAuto for that part, I’ll have to do without I guess.

This is a gap filer to reduce bubbling of the brake fluid from clutch action or fluid turbulence.