Successive writes to PEM_write_bio_X509() on same mem bio

[theactiveactor]

Does successive PEM_write_bio_X509() on the same mem bio overwrite existing data or append instead?

The context of this question is that I'm looking to be able to export/import multiple certificates in the form of one massive byte array. I plan to do so by first assembling a membio containing multiple X509 structs. If anyone has a better way to do this please let me know.

Thanks!