docs: fix links

Home.md

@@ -35,7 +35,7 @@ echo '{{"hello" | capitalize}}' | npx liquidjs
 There's [a live demo][jsfiddle] on JSFiddle, and a list of demo projects in [the demo/ directory][demo-dir]
 
 * [JSFiddle][jsfiddle]
-* [Demo for Node.js](/harttle/liquidjs/blob/master/demo/node/)
+* [Demo for Node.js](/harttle/liquidjs/blob/master/demo/nodejs/)
 * [Demo in TypeScript](/harttle/liquidjs/blob/master/demo/typescript/)
 * [Demo for Browser Usage](/harttle/liquidjs/blob/master/demo/browser/)
 * [Demo for Express.js Usage](/harttle/liquidjs/blob/master/demo/express/)
@@ -43,7 +43,7 @@ There's [a live demo][jsfiddle] on JSFiddle, and a list of demo projects in [the
 
 ## Documentation
 
-The tutorials contains a list of articles for advanced use cases, performance optimization and extending liquidjs.
+The tutorial contains a list of articles for advanced use cases, performance optimization and extending liquidjs.
 
 * [Render a Template File](/harttle/liquidjs/wiki/Render-a-File)
 * [Caching](/harttle/liquidjs/wiki/Caching)
@@ -52,7 +52,6 @@ The tutorials contains a list of articles for advanced use cases, performance op
 * [Whitespace Control](/harttle/liquidjs/wiki/Whitespace-Control)
 * [Register Filters/Tags](/harttle/liquidjs/wiki/Register-Filters-Tags)
 * [Plugins](/harttle/liquidjs/wiki/Plugins)
-* [Migrate to 9.0.0](/harttle/liquidjs/wiki/Migrate-to-9)
 
 The [API Reference](https://harttle.github.io/liquidjs/classes/_liquid_.liquid.html) provides detailed descriptions for classes, methods and properties.
 
@@ -63,4 +62,6 @@ The [API Reference](https://harttle.github.io/liquidjs/classes/_liquid_.liquid.h
 * [Truthy and Falsy](/harttle/liquidjs/wiki/Truthy-and-Falsy)
 
 [jsfiddle]: https://jsfiddle.net/x43eb0z6/
-[demo-dir]: https://github.com/harttle/liquidjs/tree/master/demo
+[demo-dir]: https://github.com/harttle/liquidjs/tree/master/demo
+[pp]: https://github.com/taylorhakes/promise-polyfill
+[caniuse-promises]: http://caniuse.com/#feat=promises

Operators.md

@@ -1,3 +1,18 @@
-Please refer to [the operators document](https://shopify.github.io/liquid/basics/operators/) from Shopify. Operators supported by LiquidJS are:
+## Operators
 
-`==`, `!=`, `>`, `<`, `>=`, `<=`, `or`, `and`, `contains`.
+Liquid operators are very simple and different. According to the [operators document](https://shopify.github.io/liquid/basics/operators/) from Shopify, there're 2 types of operators supported:
+
+* Comparison operators: `==`, `!=`, `>`, `<`, `>=`, `<=`
+* Logic operators: `or`, `and`, `contains`
+
+Thus numerical operators are not supported and you cannot even plus two numbers `{{a + b}}`. Actually `+` is a valid variable name.
+
+## Precedence
+
+The comparison operators have higher precedence than logic operators.
+
+## Associativity
+
+Logic operators are evaluated from right to left, see [shopify docs][operator-order].
+
+[operator-order]: https://help.shopify.com/en/themes/liquid/basics/operators#order-of-operations

Plugins.md

@@ -3,7 +3,9 @@ This article provides information about how to create and use a plugin
 
 ## Write a Plugin
 
-We'll make a plugin to upper case every letter of the input,
+A liquidjs plugin is simple function which takes the [Liquid class][liquid] as the first parameter and the Liquid instance for `this`. We can call liquidjs APIs on `this` to make certain changes, especially [register filters and tags][register].
+
+Now we'll make a plugin to upper case every letter of the input,
 save the following snippet to `upup.js`:
 
 ```javascript
@@ -32,11 +34,12 @@ engine
 
 ## Plugin List
 
-See <https://github.com/harttle/liquidjs#differences-and-limitations>.
+Since this library excludes certain features that are available on the Shopify platform but not on the [Shopify/liquid](https://github.com/Shopify/liquid/) repo, see <https://github.com/harttle/liquidjs#differences-and-limitations>.
 
-Since this library excludes certain features that are available on the Shopify platform but not on the [Shopify/liquid](https://github.com/Shopify/liquid/) repo, see the following plugins that backfill those features:
+Here's a list of plugins that backfill those features. Feel free to add yours, this file is publicly editable.
 
 * Sections Tags (WIP): https://github.com/harttle/liquidjs-section-tags
 * Color Filters: https://github.com/harttle/liquidjs-color-filters
 
-> Feel free to add yours, this file is publicly editable.
+[liquid]: https://harttle.land/liquidjs/classes/_liquid_.liquid.html
+[register]: /harttle/liquidjs/wiki/Register-Filters-Tags

Render-a-File.md

@@ -46,6 +46,39 @@ var engine = new Liquid({
 });
 ```
 
+## Abstract File System
+
+LiquidJS defines an abstract file system interface in [src/fs/ifs.ts][ifs] and the default implementation is [src/fs/node.ts][fs-node] for Node.js and [src/fs/browser.ts][fs-browser] for the browser bundle.
+
+The `Liquid` constructor provides a [fs][fs] option to specify the file system implementation. It's supposed to be used to define customized template fetching logic, i.e. fetch template from a database table, like:
+
+```javascript
+var engine = new Liquid({
+    fs: {
+        readFileSync (file) {
+            return db.model('Template').findByIdSync(file).text
+        },
+        await readFile (file) {
+            const template = await db.model('Template').findById(file)
+            return template.text
+        },
+        existsSync () {
+            return true
+        },
+        await exists () {
+            return true
+        },
+        resolve(root, file, ext) {
+            return file
+        }
+    }
+});
+```
+
+[fs]: https://harttle.land/liquidjs/interfaces/_liquid_options_.liquidoptions.html#fs
+[ifs]: https://github.com/harttle/liquidjs/blob/master/src/fs/ifs.ts
+[fs-node]: https://github.com/harttle/liquidjs/blob/master/src/fs/node.ts
+[fs-browser]: https://github.com/harttle/liquidjs/blob/master/src/fs/browser.ts
 [layout]: https://help.shopify.com/en/themes/liquid/tags/theme-tags#layout
 [include]: https://help.shopify.com/themes/liquid/tags/theme-tags#include
 [renderFile]: https://harttle.land/liquidjs/classes/_liquid_.liquid.html#renderfile