Merge pull request #27 from sparksuite/readme

Write the README

README.md

@@ -1,2 +1,115 @@
-# w3c-css-validator
-Validates CSS using W3C's public CSS validator service
+# W3C CSS Validator
+A modern package for validating CSS using [W3C's public CSS validator service](https://jigsaw.w3.org/css-validator/). It simplifies and standardizes the API that W3C exposes to follow newer and more JavaScript-specific conventions. The package is written entirely in TypeScript, is thoroughly tested, has zero dependencies, and uses an asynchronous design.
+
+## Getting started
+
+Install with Yarn or npm:
+
+```
+yarn add w3c-css-validator
+```
+
+```
+npm install w3c-css-validator
+```
+
+Import or require:
+
+```ts
+import validator from 'w3c-css-validator';
+```
+
+```ts
+const validator = require('w3c-css-validator');
+```
+
+Validate some CSS:
+
+```ts
+const result = await cssValidator.validateText('.foo { text-align: center; }');
+
+/*
+Result will be:
+
+{
+    valid: true,
+    errors: [],
+}
+*/
+```
+
+## `cssValidator.validateText()`
+
+This function is used to validate CSS contained within a string.
+
+###  Options
+
+You can customize the behavior with options, passed as the second argument.
+
+Option | Default | Possible values
+--- | --- | ---
+`medium` | `all` | `all`, `braille`, `embossed`, `handheld`, `print`, `projection`, `screen`, `speech`, `tty`, `tv`
+`warningLevel` | `0` | `0`, `1`, `2`, `3`
+
+Option | Explanation
+--- | ---
+`medium` | The equivalent of the `@media` rule, applied to all of the CSS
+`warningLevel` | `0` means don't return any warnings; `1`, `2`, `3` will return warnings (if any), with higher numbers corresponding to more warnings
+
+Example:
+
+```ts
+const result = await cssValidator.validateText(css, {
+    medium: 'print',
+    warningLevel: 3,
+});
+```
+
+### Response structure
+
+By default, the function returns a Promise, which resolves to an object that looks like:
+
+```ts
+{
+    valid: boolean;
+    errors: {
+        line: number;
+        message: string;
+    }[];
+}
+```
+
+If you ask it to return warnings via `warningLevel`, it will also include a `warnings` key:
+
+```ts
+{
+    ...
+    warnings: {
+		line: number;
+		level: 1 | 2 | 3;
+		message: string;
+	}[];
+}
+```
+
+## Errors vs. warnings
+
+From W3C's [manual](https://jigsaw.w3.org/css-validator/manual.html):
+
+> The validator can give you two types of messages: errors and warnings. Errors are given when the checked CSS does not respect the CSS recommendation. Warnings are different from errors since they do not state a problem regarding the specification. They are here to warn that some points might be dangerous and could lead to a strange behavior on some user agents.
+
+## Throttling
+
+You should not call the validator more often than **1 req/sec**. From W3C's [manual](https://jigsaw.w3.org/css-validator/manual.html):
+
+> If you wish to call the validator programmatically for a batch of documents, please make sure that your script will sleep for at least 1 second between requests. The CSS Validation service is a free, public service for all, your respect is appreciated. thanks.
+
+## Local development
+
+To prep a just-cloned or just-cleaned repository for local development, run `yarn dev`.
+
+To test the whole project, run `yarn test`.
+
+To format the code, run `yarn format`.
+
+To clean the repository (removes any programmatically generated files), run `yarn clean`.