Improve docs

README.md

@@ -106,13 +106,13 @@ export default {
 
 Additional configuration may be added in the future. For now, `rules` is the only useful key.
 
-### Rules
+### Rules (`rules`)
 
 All rules are optional.
 
 #### `elm`
 
-The `elm` rule specifies what elements are allowed in the SVG. It should be an object or an array of objects where:
+Rules at `elm` specify what elements are allowed in the SVG. It should be an object or an array of objects where:
 
 - The keys are the element CSS selectors. See [_Selecting elements_ on cheerio's documentation][selecting-elements-cheerio].
 - The values are either:
@@ -140,7 +140,7 @@ export default {
 
 #### `attr`
 
-The `attr` rule specifies what attributes are allowed on elements. It should be an object or an array of objects where the keys must be either:
+Rules at `attr` specify the attributes that are allowed on elements. It should be an object or an array of objects where the keys must be either:
 
 - `"rule::selector"`: The value must be the CSS selector of the element to which the rule applies. See [_Selecting elements_ on cheerio's documentation][selecting-elements-cheerio].
 - `"rule::whitelist"`: If enabled, extra attributes beyond of the ones defined in additional keys are not allowed on the element. The value must be a boolean.
@@ -187,18 +187,18 @@ export default {
 
 #### `valid`
 
-The `valid` rule specifies if the SVG is valid or not. It should be a boolean to enable or disable the rule.
+The `valid` rule is used to check that the SVG is valid using [`XMLValidator` of fast-xml-parser](https://github.com/NaturalIntelligence/fast-xml-parser/blob/HEAD/docs/v4/4.XMLValidator.md). It should be a boolean to enable or disable the rule.
 
 #### Custom rules (`custom`)
 
 Custom rules can be specified by an array of functions. Each function should have the signature `(reporter, $, ast, { filename }) => void`, where:
 
 - `reporter` is the object that will be used to report the errors.
-- `$` is the cheerio object of the SVG.
-- `ast` is the abstract syntax tree of the SVG.
-- `filepath` is the full path of the file being linted.
+- `$` is the [cheerio object](https://cheerio.js.org/docs/api/classes/Cheerio) of the SVG.
+- `ast` is the abstract syntax tree of the SVG generated by [htmlparser2](https://feedic.com/htmlparser2/).
+- `filepath` is the absolute path of the file being linted.
 
-You can set `reporter.name` to define the name of the rule shown by the output when an error is found. You can call `repoter.error(message)` to report an error.
+You can use the setter of `reporter.name` to define the name of the rule shown by the output when errors are found. You can call `repoter.error(message)` to report an error.
 
 ##### Example
 
@@ -234,7 +234,7 @@ External rules can be specified by their package name and rule name, separated b
 import("package-of-the-rule/rule-name.js");
 ```
 
-So you need to export the rule function from the file `rule-name.js` in the package `package-of-the-rule` as default to expose it.
+The rule function must be exported from the file `rule-name.js` in the package `package-of-the-rule` as the default export to expose it.
 
 ##### Example