this function is used by high level Lattice functions like
`xyplot`

to parse the formula argument and evaluate various
components of the data.

1 2 3 4 5 |

`model` |
the model/formula to be parsed. This can be in either of two
possible forms, one for 2d and one for 3d formulas, determined by
the |

`data` |
the environment/dataset where the variables in the formula are evaluated. |

`dimension` |
dimension of the model, see above |

`subset` |
index for choosing a subset of the data frame |

`groups` |
the grouping variable, if present |

`multiple, outer` |
logicals, determining how a ‘+’ in the y and x components of
the formula are processed. See |

`subscripts` |
logical, whether subscripts are to be calculated |

`drop` |
logical or list, similar to the |

returns a list with several components, including ```
left,
right, left.name, right.name, condition
```

for 2-D, and ```
left,
right.x, right.y, left.name, right.x.name, right.y.name, condition
```

for 3-D. Other possible components are groups, subscr

Saikat DebRoy, Deepayan Sarkar Deepayan.Sarkar@R-project.org

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