Logging. Message and error logging. Provides structured access to debug, information, warning and error messages from the libraries. Structured information is most often used from errors such as parsing where file or URI and line numbers can be returned via a #raptor_locator object pointer found by librdf_log_message_locator() on the #librdf_log_message. @user_data: @message: @arguments: @Returns: @user_data: @message: @Returns: @LIBRDF_LOG_NONE: @LIBRDF_LOG_DEBUG: @LIBRDF_LOG_INFO: @LIBRDF_LOG_WARN: @LIBRDF_LOG_ERROR: @LIBRDF_LOG_FATAL: @LIBRDF_LOG_LAST: @LIBRDF_FROM_NONE: @LIBRDF_FROM_CONCEPTS: @LIBRDF_FROM_DIGEST: @LIBRDF_FROM_FILES: @LIBRDF_FROM_HASH: @LIBRDF_FROM_INIT: @LIBRDF_FROM_ITERATOR: @LIBRDF_FROM_LIST: @LIBRDF_FROM_MODEL: @LIBRDF_FROM_NODE: @LIBRDF_FROM_PARSER: @LIBRDF_FROM_QUERY: @LIBRDF_FROM_SERIALIZER: @LIBRDF_FROM_STATEMENT: @LIBRDF_FROM_STORAGE: @LIBRDF_FROM_STREAM: @LIBRDF_FROM_URI: @LIBRDF_FROM_UTF8: @LIBRDF_FROM_MEMORY: @LIBRDF_FROM_LAST: @message: @Returns: @message: @Returns: @message: @Returns: @message: @Returns: @message: @Returns: