These predicate functions checks for whether a geometry varies along a given
axis. While it is common in 2 dimensions to ask whether something is vertical
or horizontal that notion does not scale well to 3 dimensions and euclid
instead elects to check for whether a given geometry is constant in a
specific coordinate value. As such, e.g. `has_constant_x()`

is equivalent to
asking whether a given 2 dimensional geometry is vertical but also works for
3 dimensional geometries.

## Arguments

- x
A geometry vector

- axis
One or more specifications of the axes to check against as

`"x"`

,`"y"`

,`"z"`

or`1`

,`2`

,`3`

## See also

Other Predicates:
`collinear()`

,
`geometry_class`

,
`geometry_turns`

,
`has_intersection()`

,
`in_order()`

,
`is_degenerate()`

,
`location_predicates`

,
`parallel()`