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PR #3676

Alternatively, if statement could be: if(substr($column->dbType, 0, 4) === 'enum'), however expected implemented option to be more robust across other database formats.

Created after followup on this issue:  https://github.com/yiisoft/yii/issues/292#issuecomment-44780779

added class references (current version without hyperlink)

- better title page,
- book style,
- improved internal linking using labels and references

fixes #2797

fixes #3539

```
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 #3551

issue #3494

without check

fixes #3438