validation draft

docs/guide/validation.md

+Model validation reference
+==========================
+
+This guide section doesn't describe how validation works but instead describes all Yii validators and their parameters.
+In order to learn model validation basics please refer to [Model, Validation subsection](model.md#Validation).
+
+Standard Yii validators
+-----------------------
+
+- `boolean`: [[BooleanValidator]]
+- `captcha`: [[CaptchaValidator]]
+- `compare`: [[CompareValidator]]
+- `date`: [[DateValidator]]
+- `default`: [[DefaultValueValidator]]
+- `double`: [[NumberValidator]]
+- `email`: [[EmailValidator]]
+- `exist`: [[ExistValidator]]
+- `file`: [[FileValidator]]
+- `filter`: [[FilterValidator]]
+- `in`: [[RangeValidator]]
+- `integer`: [[NumberValidator]]
+- `match`: [[RegularExpressionValidator]]
+- `required`: [[RequiredValidator]]
+- `string`: [[StringValidator]]
+- `unique`: [[UniqueValidator]]
+- `url`: [[UrlValidator]]
+
+TBD: refer to http://www.yiiframework.com/wiki/56/ for the format
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