Comparison of Unicode encodings
This article compares Unicode encodings in two types of environments: 8-bit clean environments, and environments that forbid the use of byte values with the high bit set. Originally, such prohibitions allowed for links that used only seven data bits, but they remain in some standards, so some standard-conforming software must generate messages that comply with the restrictions.
Source: Wikipedia — Comparison of Unicode encodings (CC BY-SA 4.0)