NML:Error

The general form of an error statement is:

error(level, message[, extra_text[, parameter1[, parameter2]]])

where level is the severity of the message and one of NOTICE, WARNING, ERROR, FATAL. The message can be either a custom defined string which can contain up to two parameters or it can be one of the pre-defined strings which already have translations. The first {STRING}-code will always be replaced by the NewGRF name. The second {STRING}-code will be replaced by the value of 'extra_text'. Extra_text can be a string defined in the language files or it can be a literal string, in which case it cannot be translated. You should only use a literal string in those cases where you are sure it doesn't have to be translated, for example to provide a version string like "0.7.0".

name	actual text	Contents of extra_text
REQUIRES_TTDPATCH	"{STRING} requires at least TTDPatch version {STRING}"	version string
REQUIRES_DOS_WINDOWS	"{STRING} is for the {STRING} version of TTD."	Windows] Palette type
USED_WITH	"{STRING} is designed to be used with {STRING}"	switchname + value, e.g. "multihead 0". This is designed to be used for incompatible settings that you can check via ttdpatch_flags.
INVALID_PARAMETER	"Invalid parameter for {STRING}: parameter {STRING} ({PARAM})"	extra_text should be the parameter number written out as string. {PARAM} is replaced by parameter1. filled in.
MUST_LOAD_BEFORE	"{STRING} must be loaded before {STRING}."	NewGRF name
MUST_LOAD_AFTER	"{STRING} must be loaded after {STRING}."	NewGRF name
REQUIRES_OPENTTD	"{STRING} requires OpenTTD version {STRING} or better."	version string
string(STR_MY_ERROR_MESSAGE)	(user-defined string)	The message-string can use the code {STRING} up to 2 times, the first usage will be replaced by the NewGRF name and the second usage by 'extra_text'. After 2 {STRING}-codes you can include up to 2 {PARAM}-codes that will be replaced by the contents of parameter1 and parameter2.

For example:

 error(NOTICE, USED_WITH, string(STR_REGRESSION_CARE));
 error(FATAL, string(STR_REGRESSION_ERROR), string(STR_ANSWER), 14, param[1] + 12 * param[2]);