How does vim determine the way the text is colored in the section of ":help group-name"?

Hi,

I see the following text in ":help group-name" colored. But when I
checked the file syntax.txt, I didn't see anything special for
indicating the colors. Could anybody let me know how vim determines
the colors? Thanks.

*Comment any comment

*Constant any constant
String a string constant: "this is a string"
Character a character constant: 'c', '\n'
Number a number constant: 234, 0xff
Boolean a boolean constant: TRUE, false
Float a floating point constant: 2.3e10

*Identifier any variable name
Function function name (also: methods for classes)

*Statement any statement
Conditional if, then, else, endif, switch, etc.
Repeat for, do, while, etc.
Label case, default, etc.
Operator "sizeof", "+", "*", etc.
Keyword any other keyword
Exception try, catch, throw

*PreProc generic Preprocessor
Include preprocessor #include
Define preprocessor #define
Macro same as Define
PreCondit preprocessor #if, #else,