Available options in the spark.read.option()
Annoyingly, the documentation for the option method is in the docs for the json method. The docs on that method say the options are as follows (key -- value -- description):

primitivesAsString -- true/false (default false) -- infers all primitive values as a string type

prefersDecimal -- true/false (default false) -- infers all floating-point values as a decimal type. If the values do not fit in decimal, then it infers them as doubles.

allowComments -- true/false (default false) -- ignores Java/C++ style comment in JSON records

allowUnquotedFieldNames -- true/false (default false) -- allows unquoted JSON field names

allowSingleQuotes -- true/false (default true) -- allows single quotes in addition to double quotes

allowNumericLeadingZeros -- true/false (default false) -- allows leading zeros in numbers (e.g. 00012)

allowBackslashEscapingAnyCharacter -- true/false (default false) -- allows accepting quoting of all character using backslash quoting mechanism

allowUnquotedControlChars -- true/false (default false) -- allows JSON Strings to contain unquoted control characters (ASCII characters with value less than 32, including tab and line feed characters) or not.

mode -- PERMISSIVE/DROPMALFORMED/FAILFAST (default PERMISSIVE) -- allows a mode for dealing with corrupt records during parsing.

PERMISSIVE : when it meets a corrupted record, puts the malformed
string into a field configured by columnNameOfCorruptRecord, and sets
other fields to null. To keep corrupt records, an user can set a
string type field named columnNameOfCorruptRecord in an user-defined
schema. If a schema does not have the field, it drops corrupt records
during parsing. When inferring a schema, it implicitly adds a
columnNameOfCorruptRecord field in an output schema.
DROPMALFORMED : ignores the whole corrupted records.
FAILFAST : throws an exception when it meets corrupted records.
When I read other people's python code, like, spark.read.option("mergeSchema", "true"), it seems that the coder has already known what the parameters to use. But for a starter, is there a place to look up those available parameters? I look up the apche documents and it shows parameter undocumented. 
Thanks.