### reference

When

**reference** is

**cell**, the plane is crystallographic
so plane indices are required and its parent must be a cell.
When

**reference** is

**atoms**, the plane is described
by real and integer polygon data inside two <data></data> blocks,
so the plane becomes independent of the atoms used to define it.

Example: **<plane ... reference="cell"/>** (default)
Allowed values: **cell**, **atoms** (optional)

### h, k, l

Set the indices

**h, k, l** defining a crystallographic plane.
The three indices cannot be all zero. An error is shown when these
indices are not indicated for a crystallographic plane or when they
are indicated for an atomic plane.

Example: **<plane ... h="1" k="0" l="0"/>** (no default)
Allowed values: integer (required, coupled)

### vectors

Set the type of cell vectors,

**conventional** or

**primitive**,
used to determine the crystallographic plane with

**h**,

**k**,

**l** indices. When the lattice is primitive there is no difference
between

**conventional** or

**primitive** cell vectors.
An error is shown when

**vectors** is set for an atomic plane.

Example: **<plane ... vectors="conventional"/>** (default)
(defined in **GAMGI_PHYS_PLANE_VECTORS**)
Allowed values: **conventional**, **primitive** (optional)

### model

An atomic plane is always represented as a

**polygon**.
A crystallographic plane can also be represented as a

**pole**, a

**trace** (for projected planes), or
a

**vector** (for reciprocal lattice planes).

Example: **<plane ... model="polygon"/>** (default)
Allowed values: **polygon**, **pole**, **trace**, **vector** (optional)