docs(attr-whitespace): initial documentation

Author: nschonni

docs/user-guide/list-rules.md

@@ -23,6 +23,7 @@ title: List of rules
 - [`attr-unsafe-chars`](/docs/user-guide/rules/attr-unsafe-chars): Attribute values cannot contain unsafe chars.
 - [`attr-value-double-quotes`](/docs/user-guide/rules/attr-value-double-quotes): Attribute values must be in double quotes.
 - [`attr-value-not-empty`](/docs/user-guide/rules/attr-value-not-empty): All attributes must have values.
+- [`attr-whitespace`](/docs/user-guide/rules/attr-whitespace): No leading or trailing spaces in attribute values.
 - [`alt-require`](/docs/user-guide/rules/alt-require): The alt attribute of an element must be present and alt attribute of area[href] and input[type=image] must have a value.
 - [`input-requires-label`](/docs/user-guide/rules/input-requires-label): All [ input ] tags must have a corresponding [ label ] tag.
 

docs/user-guide/rules/attr-whitespace.md

@@ -0,0 +1,29 @@
+---
+id: attr-whitespace
+title: attr-whitespace
+---
+
+No leading or trailing spaces inside attribute values.
+
+Level: `error`
+
+## Config value
+
+1. true: enable rule
+2. false: disable rule
+
+The following pattern are **not** considered violations:
+
+<!-- prettier-ignore -->
+```html
+<div title="a"></div>
+```
+
+The following pattern is considered violation:
+
+<!-- prettier-ignore -->
+```html
+<div title=" a"></div>
+<div title="a "></div>
+<div title =" a "></div>
+```