This is a testharness.js-based test.
PASS syntax:'*', initialValue:'a' is valid 
PASS syntax:' * ', initialValue:'b' is valid 
PASS syntax:'<length>', initialValue:'2px' is valid 
PASS syntax:' <number>', initialValue:'5' is valid 
PASS syntax:'<percentage> ', initialValue:'10%' is valid 
PASS syntax:'<color>+', initialValue:'red' is valid 
PASS syntax:' <length>+ | <percentage>', initialValue:'2px 8px' is valid 
PASS syntax:'<length>|<percentage>|<length-percentage>', initialValue:'2px' is valid 
PASS syntax:'<color> | <image> | <url> | <integer> | <angle>', initialValue:'red' is valid 
PASS syntax:'<time> | <resolution> | <transform-function> | <custom-ident>', initialValue:'red' is valid 
PASS syntax:'*', initialValue:':> hello' is valid 
PASS syntax:'*', initialValue:'([ brackets ]) { yay (??)}' is valid 
PASS syntax:'*', initialValue:'yep 'this is valid too'' is valid 
PASS syntax:'*', initialValue:'unmatched opening bracket is valid :(' is valid 
PASS syntax:'*', initialValue:'"' is valid 
PASS syntax:'<length>', initialValue:'0' is valid 
PASS syntax:'<length>', initialValue:'10px /*:)*/' is valid 
PASS syntax:'<length>', initialValue:' calc(-2px)' is valid 
PASS syntax:'<length>', initialValue:'calc(2px*4 + 10px)' is valid 
PASS syntax:'<length>', initialValue:'7.1e-4cm' is valid 
PASS syntax:'<length>', initialValue:'calc(7in - 12px)' is valid 
PASS syntax:'<length>+', initialValue:'2px 7px calc(8px)' is valid 
PASS syntax:'<percentage>', initialValue:'-9.3e3%' is valid 
PASS syntax:'<length-percentage>', initialValue:'-54%' is valid 
PASS syntax:'<length-percentage>', initialValue:'0' is valid 
PASS syntax:'<length-percentage>', initialValue:'calc(-11px + 10.4%)' is valid 
PASS syntax:'<number>', initialValue:'-109' is valid 
PASS syntax:'<number>', initialValue:'2.3e4' is valid 
PASS syntax:'<integer>', initialValue:'-109' is valid 
PASS syntax:'<integer>', initialValue:'19' is valid 
PASS syntax:'<angle>', initialValue:'10deg' is valid 
PASS syntax:'<angle>', initialValue:'20.5rad' is valid 
PASS syntax:'<angle>', initialValue:'calc(50grad + 3.14159rad)' is valid 
PASS syntax:'<time>', initialValue:'2s' is valid 
PASS syntax:'<time>', initialValue:'calc(2s - 9ms)' is valid 
FAIL syntax:'<resolution>', initialValue:'10dpi' is valid Failed to execute 'registerProperty' on 'CSS': The initial value provided does not parse for the given syntax.
FAIL syntax:'<resolution>', initialValue:'-5.3dpcm' is valid Failed to execute 'registerProperty' on 'CSS': The initial value provided does not parse for the given syntax.
FAIL syntax:'<transform-function>', initialValue:'scale(2)' is valid Failed to execute 'registerProperty' on 'CSS': The initial value provided does not parse for the given syntax.
FAIL syntax:'<transform-function>+', initialValue:'translateX(2px) rotate(20deg)' is valid Failed to execute 'registerProperty' on 'CSS': The initial value provided does not parse for the given syntax.
PASS syntax:'<color>', initialValue:'rgb(12, 34, 56)' is valid 
PASS syntax:'<color>', initialValue:'lightgoldenrodyellow' is valid 
PASS syntax:'<image>', initialValue:'url(a)' is valid 
PASS syntax:'<image>', initialValue:'linear-gradient(yellow, blue)' is valid 
PASS syntax:'<url>', initialValue:'url(a)' is valid 
PASS syntax:'banana', initialValue:'banana' is valid 
PASS syntax:'bAnAnA', initialValue:'bAnAnA' is valid 
PASS syntax:'ba-na-nya', initialValue:'ba-na-nya' is valid 
PASS syntax:'banana', initialValue:'banan\61' is valid 
PASS syntax:'<custom-ident>', initialValue:'banan\61' is valid 
PASS syntax:'big | bigger | BIGGER', initialValue:'bigger' is valid 
PASS syntax:'foo+|bar', initialValue:'foo foo foo' is valid 
PASS syntax:'banana	', initialValue:'banana' is valid 
PASS syntax:'
banana\r
', initialValue:'banana' is valid 
PASS syntax:'ba
|	na\r|nya', initialValue:'nya' is valid 
PASS syntax:'null', initialValue:'null' is valid 
PASS syntax:'undefined', initialValue:'undefined' is valid 
PASS syntax:'banana', initialValue:'banana' is valid 
PASS syntax:'banana,nya', initialValue:'banana' is invalid 
PASS syntax:'banan\61', initialValue:'banana' is invalid 
PASS syntax:'<\6c ength>', initialValue:'10px' is invalid 
PASS syntax:'<banana>', initialValue:'banana' is invalid 
PASS syntax:'<Number>', initialValue:'10' is invalid 
PASS syntax:'<length', initialValue:'10px' is invalid 
PASS syntax:'<LENGTH>', initialValue:'10px' is invalid 
PASS syntax:'< length>', initialValue:'10px' is invalid 
PASS syntax:'<length >', initialValue:'10px' is invalid 
PASS syntax:'<length> +', initialValue:'10px' is invalid 
PASS syntax:'<length>++', initialValue:'10px' is invalid 
PASS syntax:'<length> | *', initialValue:'10px' is invalid 
PASS syntax:'*|banana', initialValue:'banana' is invalid 
PASS syntax:'*+', initialValue:'banana' is invalid 
FAIL syntax:'initial', initialValue:'initial' is invalid assert_throws: function "() => CSS.registerProperty({name: '--syntax-test', syntax: syntax, initialValue: initialValue})" did not throw
FAIL syntax:'<length>|initial', initialValue:'10px' is invalid assert_throws: function "() => CSS.registerProperty({name: '--syntax-test', syntax: syntax, initialValue: initialValue})" did not throw
FAIL syntax:'<length>|INHERIT', initialValue:'10px' is invalid assert_throws: function "() => CSS.registerProperty({name: '--syntax-test', syntax: syntax, initialValue: initialValue})" did not throw
PASS syntax:'*', initialValue:'initial' is invalid 
PASS syntax:'*', initialValue:'inherit' is invalid 
PASS syntax:'*', initialValue:'unset' is invalid 
FAIL syntax:'*', initialValue:'revert' is invalid assert_throws: function "() => CSS.registerProperty({name: '--syntax-test', syntax: syntax, initialValue: initialValue})" did not throw
PASS syntax:'<custom-ident>', initialValue:'initial' is invalid 
PASS syntax:'<custom-ident>+', initialValue:'foo inherit bar' is invalid 
PASS syntax:'*', initialValue:')' is invalid 
PASS syntax:'*', initialValue:'([)]' is invalid 
PASS syntax:'*', initialValue:'whee!' is invalid 
PASS syntax:'*', initialValue:'"
' is invalid 
PASS syntax:'*', initialValue:'url(moo '')' is invalid 
PASS syntax:'*', initialValue:'semi;colon' is invalid 
PASS syntax:'*', initialValue:'var(invalid var ref)' is invalid 
PASS syntax:'*', initialValue:'var(--foo)' is invalid 
PASS syntax:'banana', initialValue:'bAnAnA' is invalid 
PASS syntax:'<length>', initialValue:'var(--moo)' is invalid 
PASS syntax:'<length>', initialValue:'10' is invalid 
PASS syntax:'<length>', initialValue:'10%' is invalid 
PASS syntax:'<length>', initialValue:'calc(5px + 10%)' is invalid 
PASS syntax:'<length>', initialValue:'calc(5px * 3px / 6px)' is invalid 
PASS syntax:'<length>', initialValue:'10em' is invalid 
PASS syntax:'<length>', initialValue:'10vmin' is invalid 
PASS syntax:'<length>', initialValue:'calc(4px + 3em)' is invalid 
PASS syntax:'<length>', initialValue:'calc(4px + calc(8 * 2em))' is invalid 
PASS syntax:'<length>+', initialValue:'calc(2ex + 16px)' is invalid 
PASS syntax:'<length>+', initialValue:'10px calc(20px + 4rem)' is invalid 
PASS syntax:'<percentage> | <length>+', initialValue:'calc(100vh - 10px) 30px' is invalid 
PASS syntax:'<length>', initialValue:'10px;' is invalid 
PASS syntax:'<length-percentage>', initialValue:'calc(2px + 10% + 7ex)' is invalid 
PASS syntax:'<percentage>', initialValue:'0' is invalid 
PASS syntax:'<integer>', initialValue:'1.0' is invalid 
PASS syntax:'<integer>', initialValue:'1e0' is invalid 
PASS syntax:'<number>|foo', initialValue:'foo var(--foo, bla)' is invalid 
PASS syntax:'<angle>', initialValue:'10%' is invalid 
PASS syntax:'<time>', initialValue:'2px' is invalid 
PASS syntax:'<resolution>', initialValue:'10' is invalid 
PASS syntax:'<transform-function>', initialValue:'scale()' is invalid 
PASS syntax:'<color>', initialValue:'fancy-looking' is invalid 
PASS syntax:'<image>', initialValue:'banana.png' is invalid 
PASS syntax:'<url>', initialValue:'banana.png' is invalid 
Harness: the test ran to completion.