added class references (current version without hyperlink)

better usage of URL in latex

bad grammar

This is probably not expected given the other naming conventions within Yii, so highlight this feature for beginners.

Looks good!

Question: Not sure about the point being made with components and
DatePicker. Please clarify if I misinterpreted.

```
vendor/bin/indent --spaces -r framework/
vendor/bin/indent --tabs -r . --pattern=*.json
vendor/bin/indent --spaces -r . --pattern=*.md
vendor/bin/indent --spaces -r . --pattern=yii.*.js
vendor/bin/indent --spaces -r . --pattern=*.css
```

fixes #3555

Typo

typo