Errors

When	Examples	What happens
Compile error	syntax error, unknown builtin, wrong argument count, undefined variable, misspelled constant, unclosed string or comment	Nothing runs. Only the first error is reported, with its line and column. The diagnostic console and the config UI's editor show it.
Builtin failure	wrong argument kind, a negative substring start, MathRandom(5, 1), an unknown message-box button name, an empty split delimiter, opening a serial port that Input.Observer already has open	The action stops at that call. Statements after it don't run, and the error is reported as BuiltinName: reason.
Soft result	operators on mismatched kinds, dividing by zero, a null or closed window (its position, size or DPI reads as 0), an index out of range, a file that isn't there, a serial port that won't open	No error. You get 0, false, "", -1 or a null Window, and the script continues.

Common compile errors and what they mean:

You wrote	Why it fails	Write instead
i++; / i += 1;	no increment or compound operators	i = i + 1;
while (x) { … }	while isn't a keyword, so it's read as an unknown function	a for loop
x = n % 2;	there's no %	x = n - (n / 2) * 2; or n & 1
'text'	single quotes aren't string delimiters	"text"
r = .5; / r = 1e3;	no leading dot, no exponents	0.5 / 1000.0
a = b = 0;	assignment isn't an expression	a = 0; b = 0;
for (;;), for (i = 0, j = 0; …)	init and step must each be one assignment	j = 0; for (i = 0; …; i = i + 1)
print(x)	unknown function. Builtin names are exact and case-sensitive.	UtilityPrint(…)
y = total + 1; as the first line	total hasn't been assigned above this point	assign it first: total = 0;