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diff --git a/heck/src/lib.rs b/heck/src/lib.rs
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+//! **heck** is a case conversion library.
+//!
+//! This library exists to provide case conversion between common cases like
+//! CamelCase and snake_case. It is intended to be unicode aware, internally,
+//! consistent, and reasonably well performing.
+//!
+//! ## Definition of a word boundary
+//!
+//! Word boundaries are defined as the "unicode words" defined in the
+//! `unicode_segmentation` library, as well as within those words in this manner:
+//!
+//! 1. All underscore characters are considered word boundaries.
+//! 2. If an uppercase character is followed by lowercase letters, a word boundary
+//! is considered to be just prior to that uppercase character.
+//! 3. If multiple uppercase characters are consecutive, they are considered to be
+//! within a single word, except that the last will be part of the next word if it
+//! is followed by lowercase characters (see rule 2).
+//!
+//! That is, "HelloWorld" is segmented `Hello|World` whereas "XMLHttpRequest" is
+//! segmented `XML|Http|Request`.
+//!
+//! Characters not within words (such as spaces, punctuations, and underscores)
+//! are not included in the output string except as they are a part of the case
+//! being converted to. Multiple adjacent word boundaries (such as a series of
+//! underscores) are folded into one. ("hello__world" in snake case is therefore
+//! "hello_world", not the exact same string). Leading or trailing word boundary
+//! indicators are dropped, except insofar as CamelCase capitalizes the first word.
+//!
+//! ### Cases contained in this library:
+//!
+//! 1. CamelCase
+//! 2. snake_case
+//! 3. kebab-case
+//! 4. SHOUTY_SNAKE_CASE
+//! 5. mixedCase
+//! 6. Title Case
+#![deny(missing_docs)]
+extern crate unicode_segmentation;
+
+mod camel;
+mod kebab;
+mod mixed;
+mod shouty_snake;
+mod snake;
+mod title;
+
+pub use camel::CamelCase;
+pub use kebab::KebabCase;
+pub use mixed::MixedCase;
+pub use shouty_snake::{ShoutySnakeCase, ShoutySnekCase};
+pub use snake::{SnakeCase, SnekCase};
+pub use title::TitleCase;
+
+use unicode_segmentation::UnicodeSegmentation;
+
+fn transform<F, G>(s: &str, with_word: F, boundary: G) -> String
+where
+    F: Fn(&str, &mut String),
+    G: Fn(&mut String)
+{
+
+    /// Tracks the current 'mode' of the transformation algorithm as it scans the input string.
+    ///
+    /// The mode is a tri-state which tracks the case of the last cased character of the current
+    /// word. If there is no cased character (either lowercase or uppercase) since the previous
+    /// word boundary, than the mode is `Boundary`. If the last cased character is lowercase, then
+    /// the mode is `Lowercase`. Othertherwise, the mode is `Uppercase`.
+    #[derive(Clone, Copy, PartialEq)]
+    enum WordMode {
+        /// There have been no lowercase or uppercase characters in the current word.
+        Boundary,
+        /// The previous cased character in the current word is lowercase.
+        Lowercase,
+        /// The previous cased character in the current word is uppercase.
+        Uppercase,
+    }
+
+    let mut out = String::new();
+    let mut first_word = true;
+
+    for word in s.unicode_words() {
+        let mut char_indices = word.char_indices().peekable();
+        let mut init = 0;
+        let mut mode = WordMode::Boundary;
+
+        while let Some((i, c)) = char_indices.next() {
+            // Skip underscore characters
+            if c == '_' {
+                if init == i { init += 1; }
+                continue
+            }
+
+            if let Some(&(next_i, next)) = char_indices.peek() {
+
+                // The mode including the current character, assuming the current character does
+                // not result in a word boundary.
+                let next_mode = if c.is_lowercase() {
+                    WordMode::Lowercase
+                } else if c.is_uppercase() {
+                    WordMode::Uppercase
+                } else {
+                    mode
+                };
+
+                // Word boundary after if next is underscore or current is
+                // not uppercase and next is uppercase
+                if next == '_' || (next_mode == WordMode::Lowercase && next.is_uppercase()) {
+                    if !first_word { boundary(&mut out); }
+                    with_word(&word[init..next_i], &mut out);
+                    first_word = false;
+                    init = next_i;
+                    mode = WordMode::Boundary;
+
+                // Otherwise if current and previous are uppercase and next
+                // is lowercase, word boundary before
+                } else if mode == WordMode::Uppercase && c.is_uppercase() && next.is_lowercase() {
+                    if !first_word { boundary(&mut out); }
+                    else { first_word = false; }
+                    with_word(&word[init..i], &mut out);
+                    init = i;
+                    mode = WordMode::Boundary;
+
+                // Otherwise no word boundary, just update the mode
+                } else {
+                    mode = next_mode;
+                }
+            } else {
+                // Collect trailing characters as a word
+                if !first_word { boundary(&mut out); }
+                else { first_word = false; }
+                with_word(&word[init..], &mut out);
+                break;
+            }
+        }
+    }
+
+    out
+}
+
+fn lowercase(s: &str, out: &mut String) {
+    let mut chars = s.chars().peekable();
+    while let Some(c) = chars.next() {
+        if c == 'Σ' && chars.peek().is_none() {
+            out.push('ς');
+        } else {
+            out.extend(c.to_lowercase());
+        }
+    }
+}
+
+fn uppercase(s: &str, out: &mut String ) {
+    for c in s.chars() {
+        out.extend(c.to_uppercase())
+    }
+}
+
+fn capitalize(s: &str, out: &mut String) {
+    let mut char_indices = s.char_indices();
+    if let Some((_, c)) = char_indices.next() {
+        out.extend(c.to_uppercase());
+        if let Some((i, _)) = char_indices.next() {
+            lowercase(&s[i..], out);
+        }
+    }
+}