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+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
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+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..566ba4d
--- /dev/null
+++ b/README.md
@@ -0,0 +1,38 @@
+# ModderBaas
+
+ModderBaas is a Rust library to interact with installed Minetest objects (worlds, games, mods), and a accompanying CLI application to manage Minetest mods on headless installations (such as `minetest-server` on Debian).
+
+## Building
+
+The build process is done through `cargo`:
+
+```
+cargo build --release
+```
+
+Library documentation can be built through
+
+```
+cargo doc
+```
+
+## Usage
+
+See `modderbaas help`.
+
+## License
+
+    Copyright (C) 2021 Daniel Schadt
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
diff --git a/src/baas.rs b/src/baas.rs
index 36a7aad..938b4c4 100644
--- a/src/baas.rs
+++ b/src/baas.rs
@@ -1,4 +1,4 @@
-//! Functions to manipulate the global Minetest installation.
+//! This module contains functions to query & manipulate the global Minetest installation.
 use std::{collections::HashMap, path::PathBuf};
 
 use dirs;
@@ -191,7 +191,8 @@ impl Baas {
 
 /// Snapshot of a [`Baas`] scan.
 ///
-/// Every item is indexed by its ID/name.
+/// A snapshot is created through the [`Baas::snapshot`] method and gives a frozen view on the
+/// installed objects.
 #[derive(Debug, Clone)]
 pub struct Snapshot {
     worlds: HashMap<String, World>,
@@ -200,14 +201,23 @@ pub struct Snapshot {
 }
 
 impl Snapshot {
+    /// Return all worlds that were found.
+    ///
+    /// The map maps the world's name to the [`World`] object.
     pub fn worlds(&self) -> &HashMap<String, World> {
         &self.worlds
     }
 
+    /// Return all games that were found.
+    ///
+    /// The map maps the game ID to the [`Game`] object.
     pub fn games(&self) -> &HashMap<String, Game> {
         &self.games
     }
 
+    /// Return the available mods that were found.
+    ///
+    /// The map maps the mod name to the [`MineMod`] object.
     pub fn mods(&self) -> &HashMap<String, MineMod> {
         &self.mods
     }
diff --git a/src/contentdb.rs b/src/contentdb.rs
index 467f9dc..d9c4688 100644
--- a/src/contentdb.rs
+++ b/src/contentdb.rs
@@ -20,16 +20,23 @@ static PROVIDES_SELECTOR: Lazy<Selector> =
 
 static A_SELECTOR: Lazy<Selector> = Lazy::new(|| Selector::parse("a").expect("Invalid selector"));
 
-/// (Partial) metadata of a content item, as returned by the Content DB.
+/// (Partial) metadata of a content item, as returned by the Content DB API.
 #[derive(Debug, Clone, PartialEq, Eq, Hash, Deserialize, Serialize)]
 pub struct ContentMeta {
+    /// Username of the author.
     pub author: String,
+    /// Name of the package.
     pub name: String,
+    /// A list of mods that are provided by this package.
     pub provides: Vec<String>,
+    /// The short description of the package.
     pub short_description: String,
+    /// The (human-readable) title of this package.
     pub title: String,
+    /// The type of the package ("mod", "game", "txp")
     #[serde(rename = "type")]
     pub typ: String,
+    /// The download URL of the package.
     pub url: Url,
 }
 
diff --git a/src/download.rs b/src/download.rs
index dfce2fc..b9507b7 100644
--- a/src/download.rs
+++ b/src/download.rs
@@ -1,3 +1,20 @@
+//! Module to download mods from the internet.
+//!
+//! This module allows to download mods from various sources in the internet. Source specification
+//! is done through the [`Source`] enum:
+//!
+//! * [`Source::Http`]: Download straight from an URL. It is expected that the URL points to a zip
+//!   archive which contains the mod, either directly or in a subfolder.
+//! * [`Source::ContentDb`]: Refers to a package on the ContentDB. The [`Downloader`] will consult
+//!   the API to get the right download URL.
+//! * [`Source::ModId`]: Refers to a simple mod name. Note that this specification can be
+//!   ambiguous, in which case the [`Downloader`] will return an error.
+//!
+//! The actual download work is done by a [`Downloader`]. Each [`Downloader`] has its own temporary
+//! directory, in which any mods are downloaded and extracted. If you drop the [`Downloader`],
+//! those mods will be deleted and the objects pointing to the now-gone directories are no longer
+//! useful.
+
 use std::{
     fs,
     io::{Cursor, Read},
@@ -54,8 +71,8 @@ impl FromStr for Source {
 
 /// A downloader is responsible for downloading mods from various sources.
 ///
-/// Note that the [`MineMod`] that the [`Downloader`] creates will not work after the downloader
-/// has been destroyed, as the temporary files will be lost.
+/// Note that the objects that the [`Downloader`] creates will not work after the downloader has
+/// been destroyed, as the temporary files will be lost.
 #[derive(Debug)]
 pub struct Downloader {
     temp_dir: TempDir,
@@ -63,10 +80,12 @@ pub struct Downloader {
 }
 
 impl Downloader {
+    /// Create a new [`Downloader`], refering to the default ContentDB.
     pub fn new() -> Result<Downloader> {
         Downloader::with_content_db(Default::default())
     }
 
+    /// Create a new [`Downloader`] that points to a specific ContentDB instance.
     pub fn with_content_db(content_db: ContentDb) -> Result<Downloader> {
         let temp_dir = TempDir::new(env!("CARGO_PKG_NAME"))?;
         Ok(Downloader {
@@ -75,6 +94,15 @@ impl Downloader {
         })
     }
 
+    /// Download a mod from the given source.
+    ///
+    /// This function may download either a mod ([`minemod::MineMod`]) or a modpack
+    /// ([`minemod::Modpack`]), therefore it returns a trait object that can be queried for the
+    /// required information.
+    ///
+    /// Note that the object will be useless when the [`Downloader`] is dropped, as the temporary
+    /// directory containing the downloaded data will be lost. Use [`ModContainer::install_to`] to
+    /// copy the mod content to a different directory.
     pub fn download(&self, source: &Source) -> Result<Box<dyn ModContainer>> {
         match *source {
             Source::Http(ref url) => self.download_http(url),
@@ -96,8 +124,7 @@ impl Downloader {
     ///
     /// The [`Downloader`] expects to receive a zipfile containing the mod directory on this link.
     ///
-    /// The mod is extracted to a temporary directory and has to be copied using
-    /// [`MineMod::copy_to`].
+    /// Refer to the module level documentation and [`Downloader::download`] for more information.
     pub fn download_http(&self, url: &Url) -> Result<Box<dyn ModContainer>> {
         let mut reader = ureq::request_url("GET", url).call()?.into_reader();
         let mut data = Vec::new();
diff --git a/src/error.rs b/src/error.rs
index 86d758f..5dbd6b6 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -1,40 +1,64 @@
+//! Error definitions for ModderBaas.
+//!
+//! The type alias [`Result`] can be used, which defaults the error type to [`enum@Error`]. Any function
+//! that introduces errors should return a [`Result`] — unless it is clear that a more narrow error
+//! will suffice, such as [`crate::util::copy_recursive`].
 use std::path::PathBuf;
 
 use thiserror::Error;
 
+/// The main error type.
 #[derive(Error, Debug)]
 pub enum Error {
+    /// A malformed or otherwise invalid mod ID has been given.
     #[error("invalid mod id '{0}'")]
     InvalidModId(String),
-    #[error("underlying HTTP error")]
-    UreqError(#[from] ureq::Error),
-    #[error("underlying I/O error")]
-    IoError(#[from] std::io::Error),
+    /// The ContentDB website returned invalid data.
     #[error("the website returned unexpected data")]
     InvalidScrape,
+    /// The directory does not contain a valid Minetest mod.
     #[error("'{0}' is not a valid mod directory")]
     InvalidModDir(PathBuf),
-    #[error("ZIP error")]
-    ZipError(#[from] zip::result::ZipError),
-    #[error("the downloaded file was empty")]
-    EmptyArchive,
+    /// The directory does not contain a valid Minetest game.
     #[error("'{0}' is not a valid game directory")]
     InvalidGameDir(PathBuf),
+    /// The directory does not contain a valid Minetest world.
     #[error("'{0}' is not a valid world directory")]
     InvalidWorldDir(PathBuf),
+    /// The directory does not contain a valid Minetest modpack.
     #[error("'{0}' is not a valid modpack directory")]
     InvalidModpackDir(PathBuf),
-    #[error("the world has no game ID set")]
-    NoGameSet,
+    /// The given source string can not be parsed into a [`crate::download::Source`].
     #[error("'{0}' does not represent a valid mod source")]
     InvalidSourceSpec(String),
-    #[error("invalid URL")]
-    UrlError(#[from] url::ParseError),
+
+    /// An empty ZIP archive was downloaded.
+    #[error("the downloaded file was empty")]
+    EmptyArchive,
+    /// The given world does not have a game ID set.
+    #[error("the world has no game ID set")]
+    NoGameSet,
+    /// ContentDB returned more than one fitting mod for the query.
     #[error("the mod ID '{0}' does not point to a single mod")]
     AmbiguousModId(String),
+
+    /// Wrapper for HTTP errors.
+    #[error("underlying HTTP error")]
+    UreqError(#[from] ureq::Error),
+    /// Wrapper for generic I/O errors.
+    #[error("underlying I/O error")]
+    IoError(#[from] std::io::Error),
+    /// Wrapper for ZIP errors.
+    #[error("ZIP error")]
+    ZipError(#[from] zip::result::ZipError),
+    /// Wrapper for URL parsing errors.
+    #[error("invalid URL")]
+    UrlError(#[from] url::ParseError),
+    /// Wrapper for Unix errors.
     #[cfg(unix)]
     #[error("underlying Unix error")]
     NixError(#[from] nix::errno::Errno),
 }
 
+/// A [`Result`] with the error type defaulted to [`enum@Error`].
 pub type Result<T, E = Error> = std::result::Result<T, E>;
diff --git a/src/game.rs b/src/game.rs
index f323212..0d2405d 100644
--- a/src/game.rs
+++ b/src/game.rs
@@ -1,3 +1,10 @@
+//! Module to interact with installed games.
+//!
+//! The main type of this module is a [`Game`], which can be constructed by opening installed
+//! Minetest games through [`Game::open`].
+//!
+//! Valid game directories have a `game.conf` configuration file which contains some metadata about
+//! the game.
 use std::{
     fmt,
     path::{Path, PathBuf},
diff --git a/src/lib.rs b/src/lib.rs
index bf9e3c9..f9b1c8b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,3 +1,51 @@
+//! ModderBaas is a library that allows you to manage Minetest mods.
+//!
+//! The main point of the library is to be used by the `modderbaas` CLI application, however it can
+//! also be used in other Rust programs that want a (limited) API to interact with Minetest
+//! content.
+//!
+//! # Representation
+//!
+//! Most objects ([`Game`], [`World`], [`MineMod`], [`Modpack`]) are represented by the path to the
+//! on-disk directory that contains the corresponding game/world/mod/modpack. The initializers take
+//! care that the directory contains a valid object.
+//!
+//! Many of the query operations do not do any caching, so avoid calling them in tight loops. If
+//! you want to do a lot of name queries (e.g. to find installed mods), consider using a
+//! [`Snapshot`].
+//!
+//! # Racing
+//!
+//! ModderBaas expects that during the time of its access, no other application meddles with the
+//! directories. It will *not* lead to crashes, but you will get a lot more error return values.
+//!
+//! # Mutability
+//!
+//! Some objects support mutating their state. This is usually done by directly writing the data
+//! into the corresponding file. Therefore, those methods (even though they mutate state) only take
+//! a shared reference (`&self`) — keep that in mind!
+//!
+//! # Crate Structure
+//!
+//! Most game objects are implemented in their own module and re-exported at the crate root:
+//!
+//! * [`game`]
+//! * [`minemod`]
+//! * [`world`]
+//!
+//! Interacting with mods from the internet/ContentDB is done through two modules:
+//!
+//! * [`contentdb`]
+//! * [`download`]
+//!
+//! Some modules contain auxiliary functions:
+//!
+//! * [`kvstore`]
+//! * [`util`]
+//!
+//! Error definitions are in [`error`].
+//!
+//! [`baas`] contains functions and data to interact with the global Minetest installation.
 use std::{fs, path::Path};
 
 use log::debug;
@@ -22,6 +70,7 @@ pub mod world;
 pub use baas::{Baas, Snapshot};
 pub use contentdb::ContentDb;
 pub use download::{Downloader, Source};
+pub use error::Error;
 pub use game::Game;
 pub use minemod::{MineMod, Modpack};
 pub use world::World;
@@ -33,6 +82,8 @@ use error::Result;
 /// Files for which `scanner` returns `Ok(..)` will be collected and returned. Files for which
 /// `scanner` returns `Err(..)` will be silently discarded.
 ///
+/// This function is useful to iterate through the items in a directory and find fitting objects:
+///
 /// ```rust
 /// use modderbaas::minemod::MineMod;
 /// let mods = scan("/tmp", |p| MineMod::open(p))?;
diff --git a/src/minemod.rs b/src/minemod.rs
index f45b897..456d1c6 100644
--- a/src/minemod.rs
+++ b/src/minemod.rs
@@ -1,3 +1,27 @@
+//! Module to interact with installed mods and modpacks.
+//!
+//! Due to technical reasons (`mod` being a Rust keyword), this module is called `minemod` and the
+//! mod objects are called [`MineMod`].
+//!
+//! Simple mods are represented by [`MineMod`], which can be opened by [`MineMod::open`]. Valid
+//! mods are identified by their `mod.conf`, which contains metadata about the mod.
+//!
+//! Modpacks can be represented by [`Modpack`] and loaded through [`Modpack::open`]. A modpack is
+//! just a collection of mods grouped together, and the modpack directory needs to have a
+//! `modpack.conf` in its directory.
+//!
+//! # Mods and Packs United
+//!
+//! In some cases, we cannot know in advance whether we are dealing with a mod or a modpack (e.g.
+//! when downloading content from ContentDB). Therefore, the trait [`ModContainer`] exists, which
+//! can be used as a trait object (`Box<dyn ModContainer>`). It provides the most important methods
+//! and allows downcasting through `Any`.
+//!
+//! If you want to work with the mods directly, you can use [`ModContainer::mods`], which returns
+//! the mod itself for [`MineMod`]s, and all contained mods for [`Modpack`]s.
+//!
+//! If you want to open a directory as a [`ModContainer`], you can use [`open_mod_or_pack`].
+
 use std::{
     any::Any,
     collections::HashMap,
@@ -20,6 +44,7 @@ pub struct MineMod {
 }
 
 impl MineMod {
+    /// Opens the given directory as a mod.
     pub fn open<P: AsRef<Path>>(path: P) -> Result<MineMod> {
         MineMod::open_path(path.as_ref())
     }
@@ -93,6 +118,7 @@ pub struct Modpack {
 }
 
 impl Modpack {
+    /// Opens the given directory as a modpack.
     pub fn open<P: AsRef<Path>>(path: P) -> Result<Modpack> {
         Modpack::open_path(path.as_ref())
     }
@@ -154,6 +180,8 @@ impl fmt::Display for Modpack {
 }
 
 /// A thing that can contain mods.
+///
+/// This is useful for code that should deal with both mods and modpacks.
 pub trait ModContainer: Any + fmt::Display {
     /// Returns the name of the mod container.
     fn name(&self) -> Result<String>;
diff --git a/src/util.rs b/src/util.rs
index d5f9ec2..ea401ba 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -1,3 +1,4 @@
+//! Utility functions.
 use std::{fs, io, path::Path};
 
 #[cfg(unix)]
diff --git a/src/world.rs b/src/world.rs
index 31ddbd4..5dce6d0 100644
--- a/src/world.rs
+++ b/src/world.rs
@@ -1,3 +1,6 @@
+//! Module to interact with Minetest worlds (savegames).
+//!
+//! The main object is [`World`], which represents a Minetest world on-disk.
 use std::{
     collections::HashMap,
     fmt,
@@ -17,6 +20,7 @@ pub struct World {
 }
 
 impl World {
+    /// Open the given directory as a [`World`].
     pub fn open<P: AsRef<Path>>(path: P) -> Result<World> {
         World::open_path(path.as_ref())
     }