Leading and trailing space on the keyword is ignored. Leading tabs on the keyword are ignored.
Correct separator
Currently the Arduino IDE requires each field to be separated by a single true tab. Spaces may be allowed as separators in a future IDE release (https://github.com/arduino/Arduino/pull/7245) but this will still apply to previous IDE versions.
It is common to see multiple tabs used in an attempt to "prettify" keywords.txt by aligning fields into columns and, at a glance, this appears to work but in fact it will cause keywords to be colored according to editor.function.style regardless of the identifier used because each field is separated by a tab. Two tabs just results in a null value for the field.
Correct identifier
There are actually two keyword identifier fields, each with their own valid identifiers. When an unrecognized identifier is encountered the Arduino IDE 1.6.5 and newer colors the keyword according to editor.function.style (as used by KEYWORD2, KEYWORD3, LITERAL2); Arduino IDE 1.6.4 and older does not color it.
KEYWORD_TOKENTYPE
KEYWORD1
KEYWORD2
KEYWORD3
LITERAL1
LITERAL2
RSYNTAXTEXTAREA_TOKENTYPE
RESERVED_WORD
RESERVED_WORD_2
DATA_TYPE
PREPROCESSOR
LITERAL_BOOLEAN
With Arduino IDE 1.6.5 and newer, the identifier must not have leading space or it is not recognized (and thus the default editor.function.style is used). With Arduino IDE 1.6.4 and older leading space on the identifier is ignored. Trailing space on the identifier is ignored.
Reference link
The REFERENCE_LINK field provides the filename of the Language reference page, which is located in {Arduino IDE installation folder}/reference/www.arduino.cc/en/Reference/. This page may be opened from the Arduino IDE via right click > Find in Reference or Help > Find in Reference. It's fairly common to see library authors add a REFERENCE_LINK value in their keywords.txt when no reference page of that name exists. Most likely this is due to them using one of the Arduino library keywords.txt as a reference without fully understanding the purpose of the field (unsurprising since it's undocumented)(has since been documented).
Leading/trailing spaces are removed from REFERENCE_LINK.
Is REFERENCE_LINK case-sensitive?
Filename
Spelling the keywords.txt filename with other case will cause it to not be recognized on filename case sensitive OSs such as Linux.
per1234
commented
6 years ago
Correct format:
KEYWORD\tKEYWORD_TOKENTYPE\tREFERENCE_LINK\tRSYNTAXTEXTAREA_TOKENTYPELeading and trailing space on the keyword is ignored. Leading tabs on the keyword are ignored.
Correct separator
Currently the Arduino IDE requires each field to be separated by a single true tab. Spaces may be allowed as separators in a future IDE release (
https://github.com/arduino/Arduino/pull/7245) but this will still apply to previous IDE versions.It is common to see multiple tabs used in an attempt to "prettify" keywords.txt by aligning fields into columns and, at a glance, this appears to work but in fact it will cause keywords to be colored according to
editor.function.styleregardless of the identifier used because each field is separated by a tab. Two tabs just results in a null value for the field.Correct identifier
There are actually two keyword identifier fields, each with their own valid identifiers. When an unrecognized identifier is encountered the Arduino IDE 1.6.5 and newer colors the keyword according to
editor.function.style(as used byKEYWORD2,KEYWORD3,LITERAL2); Arduino IDE 1.6.4 and older does not color it.KEYWORD_TOKENTYPEKEYWORD1KEYWORD2KEYWORD3LITERAL1LITERAL2RSYNTAXTEXTAREA_TOKENTYPERESERVED_WORDRESERVED_WORD_2DATA_TYPEPREPROCESSORLITERAL_BOOLEANWith Arduino IDE 1.6.5 and newer, the identifier must not have leading space or it is not recognized (and thus the default
editor.function.styleis used). With Arduino IDE 1.6.4 and older leading space on the identifier is ignored. Trailing space on the identifier is ignored.Reference link
The
REFERENCE_LINKfield provides the filename of the Language reference page, which is located in {Arduino IDE installation folder}/reference/www.arduino.cc/en/Reference/. This page may be opened from the Arduino IDE via right click > Find in Reference or Help > Find in Reference. It's fairly common to see library authors add aREFERENCE_LINKvalue in their keywords.txt when no reference page of that name exists. Most likely this is due to them using one of the Arduino library keywords.txt as a reference without fully understanding the purpose of the field(unsurprising since it's undocumented)(has since been documented). Leading/trailing spaces are removed fromREFERENCE_LINK.Is
REFERENCE_LINKcase-sensitive?Filename
Spelling the keywords.txt filename with other case will cause it to not be recognized on filename case sensitive OSs such as Linux.
Notes