Three other location methods are defined in the TEI extended pointer syntax, specifically for non-SGML data and for HyTime conformant data. The SPACE keyword may be used to address locations in space; the FOREIGN keyword may be used to address locations in terms of some external notation not defined by the Guidelines; the HYQ keyword may be used to supply a HyTime query expression. The FOREIGN and HYQ keywords are not further described here. (The latter is obsolete, while the former is largely of documentary use only).
The SPACE keyword takes either two or three parameters. The first is a name for the co-ordinate system in use: it will typically be a string like `2D' (two dimensional) or `3D'(three dimensional). The second and third parameters consist of a list of numerical values giving co-ordinate values as measured along each dimension of a Cartesian space with all axes orthogonal. The number of values is equal to the number of axes (usually 2 or 3). If only the second parameter is given, the location indicated is a point in the co-ordinate system. For example:
<xptr from='SPACE (2d) (0 0)'>indicates the origin of a two dimensional space.
If the third parameter is present, the location indicated is the rectangular prism defined by treating corresponding items from the two lists as inclusive bounds along each dimension in turn. For example
<xptr from='SPACE (2d) (0 0) (1 1)'>indicates a single unit square tangential to the origin of a two dimensional space.