In Qt how do QTextCodec::codecForName(“UTF-16”) and codecForName(“UTF-32”) decide the endianness to use?

Question

In the Qt documentation it states that (among others) the following Unicode string encodings are supported:

• UTF-8
• UTF-16
• UTF-16BE
• UTF-16LE
• UTF-32
• UTF-32BE
• UTF-32LE

Due to the three different codecs listed for 2 and 4 octet encoded Unicode, I was wondering: how do the two non-endian codecs ("UTF-16" and "UTF-32") decide which endianness to use?