symfony/symfony#17578 introduces the possibility to customise the dumped YAML string by passing a bit field of dumper flags.

Symfony 3.1 introduces quite some options that you can use to customise the behaviour of both the parser and the dumper (and also added some more additional features):

• Yaml::DUMP_OBJECT toggles object support in the dumper ([Yaml] dump customization option with dumper flags symfony#17578)
• Yaml::PARSE_EXCEPTION_ON_INVALID_TYPE, Yaml::PARSE_OBJECT, and Yaml::PARSE_OBJECT_FOR_MAP replace the previous boolean arguments of the YAML parser ([Yaml] introduce flags to customize the parser behavior symfony#17730)
• Yaml::DUMP_EXCEPTION_ON_INVALID_TYPE replaces the old boolean parameter ([Yaml] dumper flag for enabling exceptions on invalid type symfony#17743)
• parse and dump DateTime instances ([Yaml] support to parse and dump DateTime objects symfony#17836)
• Support for parsing and dumping base64 encoded binary data ([Yaml] add support for parsing the !!binary tag symfony#17863).
• dump PHP objects as YAML maps ([Yaml] add option to dump objects as maps symfony#17728)
• option to dump multi line strings as literal scalar blocks ([Yaml] option to dump multi line strings as scalar blocks symfony#17943)