In the chapter of Error Handling, where every error component is listed, it states that every error can be divided to the Error type and Error subtype. Errors directly mirrors exceptions that are thrown in execution of Apex code of the MIP package. MIP divides GraphQL related exceptions into two major types: GraphQLException and GraphQLSyntaxErrorException.
This is considered primary type of error and is covering largest area of codebase. It also wraps any errors occured on the Salesforce side, and display them as GraphQLException with corresponding errorSubType so that it is easily known if the error is forwarded from the Salesforce or not.
OperationTypeError: thrown if the document requests for the operation type not yet implemented.
SalesforceQueryError: thrown if any error occured during executing the query on the Salesforce side
DocumentError: any document related error in general
ObjectNameError: thrown for any mistyped object name, parent-child relationship name that is not correct or anything object related
VariableError: thrown for variable mistypes, not stating the variables correctly, missing variable in the variable map and similair
On the other hand,GraphQLSyntaxErrorException is related to errors that occured during lexing and parsing of the query itself. Any mistyped keywords, omitted brackets unvalid characters and similair will result in this error type.
CharacterError: any error related to the specific character not being expected in the certain place.
TokenKindError: any error related to the specific Token, not recognized as the kind it needs to be