Mark Nelson b62b5879af MDL-56046 core_dataformat: added functions to support multiple sheets
Also removed write_header() and write_footer(). The reason for this
is because in core we want to know if the format being used supports
multiple sheets. To do this, and ensure we do not break third-party
dataformat plugins, we are using method_exist(). If write_header()
and write_footer() remain in the base class then this will always
be true.
2017-06-26 13:29:32 +08:00
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