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. As of version 2.0.0.0, it does this through Myst Library's symbol JSON system.The only required mods are Mystcraft and Myst Library.
Pages also includes a new creative item: the Block Writer. When you use it on a block, it allows you to tweak and export that block as json so that it can be imported by Myst Library to use as a page in-game. You must restart to have any new pages loaded in.
Be sure to check out these other great Mystcraft add-ons: More Mystcaft, Linking Through the Ages, linking-tweaks, and mystcraft-info.
