Pages is a mod that adds, um—pages—to Mystcraft. Currently it adds several hundred blocks from vanilla Minecraft as well as the following mods: Applied Energistics 2, Biomes o' Plenty, Botania, Ender IO, Extra Utilities 2, Immersive Engineering, RFTools, Thaumcraft, Thermal Foundation, Tinkers' Construct, and The Twilight Forest. The only required mod is Mystcraft.
If you want to add a page for a block for everyone to enjoy, please make a pull request on GitHub. For information about how to use the old CSV format for 1.2.2 and below, see CSV. For information about how to use the new JSON format for 1.3.0 and above, see JSON.
Pages also supports easy editing of pages in your personal Minecraft instance. Simply head to config/pages and you'll find blocks_[mod].json and blocks_custom.json, which you can edit directly. It is recommended that any blocks you add be added to blocks_custom.json. It will be loaded first, so it will take precedence if the same blockstate exists in another file.