docs: Comparison with other tools

Fixes #12

README.md

@@ -8,6 +8,8 @@
 ![License](https://img.shields.io/crates/l/defenestrate.svg)
 [![Crates Status](https://img.shields.io/crates/v/defenestrate.svg)](https://crates.io/crates/defenestrate)
 
+## [About](docs/about.md)
+
 ## Install
 
 For now, `rust` is required for install:

docs/about.md

@@ -0,0 +1,58 @@
+# About defenestrate
+
+## Design Requirements
+
+Spell checks source code:
+- Requires special word-splitting logic to handle situations like hex (`0xDEADBEEF`), `c\nescapes`, `snake_case`, `CamelCase`, `SCREAMING_CASE`, and maybe `arrow-case`.
+- Each programming language has its own quirks, like abbreviations, lack of word separator (`copysign`), etc
+- Backwards compatibility might require keeping misspelled words.
+- Case for proper nouns is irrelevant.
+
+Checking for errors in a CI:
+- No false-positives.
+- On spelling errors, sets the exit code to fail the CI.
+
+Quick feedback and resolution for developer:
+- Fix errors for the user.
+- Integration into other programs, like editors:
+  - `fork`: easy to call into and provides a stable API, including output format
+  - linking: either in the language of choice or bindings can be made to language of choice.
+
+## Design Trade Offs
+
+### defenestrate uses a blacklist
+
+Blacklist: Known typos that map to their corresponding word
+- Ignores unknown typos
+- Ignores typos that follow c-escapes if they aren't handled correctly
+
+Whitelist: A confidence rating is given for how close a word is to one in the whitelist
+- Sensitive to false positives due to hex numbers and c-escapes
+- Traditional spell checkers use a whitelist.
+
+## Related Spell Checkers
+
+|               | defenestrate         | [scspell3k] | [bloom42/misspell][misspell-rs] | [client9/misspell][misspell-go] |
+|---------------|----------------------|-------------|---------------------------------|---------------------------------|
+| "Runtime"     | Rust ([#18][def-18]  | Python      | Rust                            | None                            |
+| Dictionary    | Blacklist            | Whitelist   | Blacklist                       | Blacklist                       |
+| Custom Dict   | No ([#9][def-9]      | Yes         | No                              | ?                               |
+| Per-Lang Dict | No ([#14][def-14]    | Yes         | No                              | ?                               |
+| CamelCase     | Yes                  | Yes         | No                              | ?                               |
+| snake_case    | Yes                  | Yes         | No                              | ?                               |
+| Ignore Hex    | No ([#19][def-19]    | Yes         | No                              | ?                               |
+| C-Escapes     | No ([#20][def-3]     | Yes         | No                              | ?                               |
+| Encodings     | UTF-8 ([#17][def-17] | Auto        | UTF-8                           | ?                               |
+| API           | Rust / [JSON Lines]  | None        | Rust                            | ?                               |
+| License       | MIT | Apache         | GPLv2       | AGPL                            | MIT                             |
+
+[JSON Lines]: http://jsonlines.org/
+[scspell3k]: https://github.com/myint/scspell
+[misspell-rs]: https://gitlab.com/bloom42/misspell
+[misspell-go]: https://github.com/client9/misspell
+[def-9]: https://github.com/epage/defenestrate/issues/9
+[def-14]: https://github.com/epage/defenestrate/issues/14
+[def-17]: https://github.com/epage/defenestrate/issues/17
+[def-18]: https://github.com/epage/defenestrate/issues/18
+[def-19]: https://github.com/epage/defenestrate/issues/19
+[def-3]: https://github.com/epage/defenestrate/issues/3