> ## Documentation Index
> Fetch the complete documentation index at: https://docs.loft.build/llms.txt
> Use this file to discover all available pages before exploring further.
# Opening
```loft theme={"theme":{"light":"github-light","dark":"github-dark"},"languages":{"custom":["/languages/loft.json","/languages/loft-fragment.json"]}}
opening O1 in wall.W1 at 4' width 3'-0" height 7'-0"
```
Since v0.3 `opening` is also a placeable category in its own right —
the type-less, filler-less cutter (SPEC-v0.3 §6.2). The standalone
element projects exactly this base interface and nothing more; doors
and windows inherit it and add their refinements on their own pages.
**Placement:** hosted — `in wall.W1 at 4'`. The station may measure from a
reference (`past` / `short of`) and land `to jamb`, `to jamb.far` or
`to centerline`.
## Parameters
| Word | Accepts | Required | Meaning |
| ------------------------------ | ----------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `in`
`in wall.W1` | a wall | instance · required | the host wall |
| `at`
`at 4'` | length | instance · required | the station along the host, from its start — or from a reference (`past` / `short of`), landing `to jamb`, `to jamb.far`, or `to centerline`
the station's reference words are their own rows — `past`, `short` — and the value is a length along the host, so `door.D1.jamb.far + 2'` composes here |
| `past`
`past grid.A` | plane (normal xy) | instance · optional | the datum the station measures forward from |
| `short`
`short of grid.B` | plane (normal xy) | instance · optional | the datum the station measures back from
spelled `short of`: `at short of ` |
| `width`
`width 3'-0"` | length | instance · required | the clear width — a hole has no type to carry it |
| `height`
`height 7'-0"` | length | instance · required | the clear height — a hole has no type to carry it |
| `sill`
`sill 3'` | length | instance · required · default: the host level + 0'
**practice** — a hole with no sill is a passage, the commonest opening of all — decision 84; the window refines `sill` to required with no default (decision 82, D0272) because a 0' window sill is never intended | the bottom of the opening, up from the host level
`sill 3'` reads as `sill + 3'`; a value below the level is legal (the anchor spelling that writes one is parked — PARKINGLOT "ẑ anchors everywhere"). |
### Reserved
| Word | Rung | Meaning | Arrives with |
| ------------ | -------- | ----------------------------------------- | ---------------------------------------------------------------------------------------------------------------- |
| `label` | instance | what the tag prints when it is not the id | a bubble or tag printing text other than the id — the grid's bubble is the one that ships |
| `phase` | instance | the phase this element is created in | the phasing era — phases are an ordered list declared in their own file, and a view looks at the model as of one |
| `demolished` | instance | the phase this element is demolished in | the phasing era — phases are an ordered list declared in their own file, and a view looks at the model as of one |
## Datums
| Datum | Shape | Status | Resolution | Rule |
| --------------------------------- | ---------- | ------ | ------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `centerline` / `cl` | plane | core | intrinsic | Station of the opening's center along the host wall — the spelling for center-to-center measurements (`at 4' past door.D1.centerline`, or `door.D1.cl` — decision 65). A BARE element ref measures clear of the facing jamb instead (decision 46). |
| `head` | plane | core | intrinsic | ẑ position of the top of the opening. |
| `sill` | plane | core | intrinsic | ẑ position of the bottom of the opening, an anchor plus offset: `sill 3'` reads `sill + 3'`. Defaults to the host level (see Default values); a value below the level is legal. Doors and bare openings inherit the default; the window refinement overrides it (below). |
| `jamb` (pair) | plane (×2) | core | — (selected) | The two jamb planes project once; a reference picks one through a selector below. |
| `jamb` / `jamb.near` / `jamb.far` | plane | core | geometric | Two spellings, two frames (decision 37). Qualified `jamb.near`/`jamb.far` are framed by the HOST WALL — `near` toward its start, `far` toward its end, the same origin `at` measures from — so they need no direction word, mean the same thing in every slot, and read as English does ("2' past D1's far jamb"). Bare `jamb` stays the geometric selector (decision 26's tape rule): whichever jamb the measurement reaches first — the one nearer the reference measured from — which changes ends with `past` vs `short of` and therefore requires a direction. Both are swing-invariant. As stations they are lengths from the host wall's start, so they compose in that wall's own `at` expressions (`door.D1.jamb.far + 2'`). |
## Roles
None — this category draws no parts of its own.