What is the format of the RDS Data API schema parameter

The batch_execute_statement function in Boto3 for the RDS Data API has a schema argument that can be passed in (see below) however it doesn't seem to have any affect on the output. Does anyone know what this field should contain? AWS docs are very vague and simply say "The name of the database schema". Any help is much appreciated!

client.batch_execute_statement(
    database='string',
    parameterSets=[
        ...
    ],
    resourceArn='string',
    schema='string',
    secretArn='string',
    sql='string',
    transactionId='string'
)