This character is a Other Letter and is mainly used in the Arabic script.
The glyph is not a composition. It has no designated width in East Asian texts. In bidirectional text it is written as Arabic letter from right to left. When changing direction it is not mirrored. The word that U+0671 forms with similar adjacent characters prevents a line break inside it. The glyph can be confused with 2 other glyphs.
The Wikipedia has the following information about this codepoint:
The waṣla (Arabic: وَصْلَة, lit. 'an instance of connection') or hamzatu l-waṣli (هَمْزَةُ ٱلْوَصْلِ, 'hamza of connection') is a variant of the letter hamza (ء) resembling part of the letter ṣād (ص) that is sometimes placed over the letter ʾalif at the beginning of the word (ٱ). The ʾalif with waṣla over it is called the ʾalifu l-waṣli (أَلِفُ ٱلْوَصْلِ, 'aleph of connection'). It indicates that the alif is not pronounced as a glottal stop (written as the hamza), but that the word is connected to the previous word (like liaison in French). Outside of vocalised liturgical texts, the waṣla is usually not written.