Age Creation

Ages, in Mystcraft, are minecraft dimensions that are characterized by a type of landscape, a collection of terrain alterations (such as caves), a collection of landscape populators (such as mineshafts), a collection of biomes and how they are distributed, a list of Celestials (such as suns, moons, stars, etc. -- note the plural form), and information about the colors, speeds, frequencies, etc. of everything.

Creating an age refers to writing a description of that age, and then making it in-game.

Age descriptions can be inconsistent; specifying two different types of biomes, for example, will cause a contradiction. This will generate instability.

Age descriptions can be incomplete; missing information will be filled in by the game during initial generation of the age. In prior versions, this would cause instability; in the current version, it does not.

Age descriptions can contain "excess" -- things like extra deposits of minerals. These will cause instability. Note that even good writing cannot prevent random additions that may contain such extras; it is possible to reduce the chance of random extras, but it is not possible to eliminate them completely.

Singletons
A fully specified world will have exactly one of each of these:

Lists
There can be zero to many of each of these. Note that writing zero does not mean that the final age will have zero.

Celestials
Suns, moons, and stars all have an explicit "dark" form. This will prevent them from having any graphical display, and permits writing ages that look like they have zero suns, or zero moons, or zero stars.

Visuals and colors
Many color aspects can be changed or adjusted. Things like leaf colors, grass color, sky color, fog color, etc. "Natural" color options exist for each of these, and that will result in normal biome coloring.

Additional stuff, such as boundless skies (no horizon line), or rainbows, can be added as well.

Alterations
There is roughly a 90% chance of one being provided if you do not list any.

Populators
There is roughly a 100% chance of potentially many being provided if you do not list any.

Effects
Some types of Instability can be explicitly written in. These will add some stability, but in general just make the world look strange, or behave oddly. Useful for keeping people out of your base in fear if you know what you are doing.