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x y is by default interpreted as VerticalSeparator[x, y].
Used in mathematics for many purposes, including indicating restriction and standing for "such that".
Also used to separate arguments of various mathematical functions.
Extensible character; grows by default to limited size.
Not the same as \[VerticalBar], which is drawn shorter.
Not the same as \[LeftBracketingBar] and \[RightBracketingBar], which are drawn with a small tee to indicate their direction.
Not the same as \[VerticalLine], which is a letter-like form, and is indefinitely extensible.
See The Mathematica Book: Section 1.10.8 and Section 3.10.4.
See also: \[RawVerticalBar] , \[NotVerticalBar] , \[DoubleVerticalBar] , \[Colon] , \[SuchThat] , \[HorizontalLine] .