useOuterStrips2: Put Strips on the Boundary of a Lattice Display.
In rjbgoudie/parental: Light-weight graph package

Try to update a "trellis" object so that strips are only shown on the top and left boundaries when printed, instead of in every panel as is usual. This version extend the version in LatticeExtra to allow more than two conditioning variables.

  useOuterStrips2(x, strip = strip.default2, strip.left =
  strip.custom2(horizontal = horizontal), top = 1,
  strip.lines = 1, strip.left.lines = strip.lines,
  horizontal = F)

`x`	An object of class "trellis".
`strip`	A function, character string, or logical that would be appropriate strip and strip.left arguments respectively in a high level lattice function call (see xyplot). Note, however, that the strip function must be of the form of strip.default2. The equivalent of strip.custom here is strip.custom2.
`strip.left`	As strip, for the strips down the left.
`top`	Determines the number of strips that are drawn along the top of the plot. Conditioning variables 1, ..., top will be displayed along the top of the plot (using strip), and variables top + 1, ..., dim(x) will be displayed along the left hand side of the plot.
`strip.lines`	height of strips in number of lines; helpful for multi-line text or mathematical annotation in strips.
`strip.left.lines`	As strip.lines, for strips down the left.
`horizontal`	...