Changing Precedences in Notations
You can isolate the elements around an operator or expression by surrounding the operator or expression with a box structure that isolates its contents (cf. the table above). The box structure typically used to do this encapsulation / isolation is the TagBox. Furthermore it is possible to change the precedence of an operator through the use of the TagBox option SyntaxForm. More will be said on this later in the section Complex Patterns and Advanced Features.
The underlying box structure of has an embedded TagBox.
The embedded TagBox in is necessary for several reasons: to contain the StyleBox asserting ZeroWidthTimes, to suppress the natural prefix operator grouping of , and to allow the parsing and formatting rules to act on an encapsulated unit.