Examples in other pages of documentation here are still using version 3 so are incompatible with the updated demo map and app. The algorithm is the same but uses the alphabet "6789B5NPQC4MXRD3LWTF2KJHG".
As well as being a geolocation code for a single point, the OpenPostcode's variability in precision lends itself immediately to describing regular and irregular areas. Using a simple syntax, complex areas made up of multiple locations and ranges of locations can be described extremely efficiently and easily. It is the only geolocation code for Ireland capable of describing and mapping irregular areas.
Areas, towns, regions, etc., can be closely defined as sets of regular or irregular length codes; for example, Mallow town might be loosely described as: MXV to MXX & T64 to T66, or as more efficiently "MXV:T66". Depending on purpose one would refine it - adding outcrops, subtracting nooks.
A complex example, just to demonstrate the syntax, although awkward, describes the Great Blasket: R32T::V,:7F,:72::9,~757,~F2,R2D9::K,:G,:L::P,:R::T,:CX,~J65::6,~K222
Or all the NCT centres in the country: NCT Centres