Sprite Attribute 3 Register

Number	TBRegisterNumber::$38
Readable	TBRegisterReadable::No
Writable	TBRegisterWritable::Yes
Short Description	[[ShortDesc::Nextreg port-mirror to write directly into "byte 4" of {{#ask: PortNumber::$xx57 }} ($xx57{{#ask: PortNumber::$xx57 |mainlabel=- |headers=hide |intro= /  |?NumberDec#- }}).]]

Byte 4 is bitmapped:

Bit	Description
7	Enable visibility
6	? see note below.
5-0	Pattern index ("Name")

Bit 6 is in normal port writing used to indicate there will be "byte 5" following, while with NextReg mirror the "byte 5" is directly accessible at {{#ask: TBRegisterNumber::$39 }} ($39). At the time of adding this documentation, it is not clear what bit 6 does here, but value "0" may work as "reset whole byte 5 to zero", so if you intend to use extended "byte 5" features, write "1" or test with actual HW. And other way too, if you don't plan to use the extra features, probably write zero to {{#ask: TBRegisterNumber::$39 }} ($39) explicitly, even if you use "0" for bit 6 here.