[Freeciv-Dev] proposed ZOC doc

[David Pfitzner <dwp@xxxxxxxxxxxxxx>]

I propose the following as ZOC helptext.  It documents the current
freeciv ZOC rules, with a note at the end about future changes.

Any corrections/clarifications/etc ?

-- David

%% Notice! no line may be more than 68 chars wide: --------------->|

Zone of Control, abbreviated as ZOC, is the effect that your land 
units cannot move freely in zones controlled (or partially 
controlled) by enemy forces.

The general rule is that a land unit which is adjacent to an enemy 
occupied square cannot move directly to another square which is 
also adjacent to an enemy occupied square.  Here an enemy occupied 
square means an enemy city, or an enemy unit on a land square.
Adjacency means any of the eight squares surrounding a unit.

In the following special cases ZOC does not apply:
- A unit moving directly into or out of a city.
- A unit moving onto a square occupied by a friendly unit.
- A unit type which explicitly ignores ZOC, eg Diplomats.

Note:
- Only land units are restricted by ZOC.
- Non-land units can impose ZOC (that is, count as enemy occupied 
  squares), but only if they are on a land square.  So effectively
  sea units cannot impose ZOC, and air units (including helicopters)
  do not impose ZOC if they are over sea squares.
- ZOC does not restrict unit attacks, only movement.

TIP: You can infiltrate enemy zones by first moving in a Diplomat
(or some other unit which ignores ZOC), and then moving regular
units onto the square now occupied by the Diplomat.  By repeating
this process (and optionally leaving some units behind to keep 
squares occupied), you can make a path through enemy territory.

The following Freeciv ZOC effects differ from some similar games:
- Enemy cities with no units in them impose ZOC;
- Land units moving from boats at sea onto land are subject to ZOC.
These cases will probably be changed in a future version of Freeciv.