In TAP v13 and higher, the specification says the first line must be:
or similar. Some TAP consumers (notably Meson) emit warnings if this line is not emitted.
I personally think Meson is wrong to warn on this, because a TAP stream without this first line is not valid TAP v13, but is perfectly valid TAP v12 - but the warnings are quite visible and could mislead bug reporters into thinking tests that use TAPTestRunner are broken.