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run code in 200+ php & hhvm versions
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<?php mb_internal_encoding('UTF-8'); echo 'Subject: ', mb_encode_mimeheader('訂購網', 'UTF-8', 'B');
based on 2Ap1d
Output for 5.3.18 - 7.3.0rc3
Subject: =?UTF-8?B?6KiC6LO857ay?=