The glyph is not a composition. Its width in East Asian texts is determined by its context. It can be displayed wide or narrow. In bidirectional text it is written from left to right. When changing direction it is not mirrored. The word that U+03BE forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with 5 other glyphs.
The Wikipedia has the following information about this codepoint:
Xi (UK: , US: ; uppercase Ξ, lowercase ξ; Greek: ξι) is the fourteenth letter of the Greek alphabet, representing the voiceless consonant cluster [ks]. Its name is pronounced [ksi] in Modern Greek. In the system of Greek numerals, it has a value of 60. Xi was derived from the Phoenician letter samekh .
Xi is distinct from the letter chi, which gave its form to the Latin letter X.