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=== Tag Library Usage


A tag library fulfills role of "view helper" in the Model View Controller (MVC) pattern and helps with GSP rendering. In Grails a tag library is a class with a name that ends in the convention "TagLib" and lives in the `grails-app/taglib` directory. Use the link:../Command%20Line/create-taglib.html[create-taglib] command to create a tag library:

[source,groovy]
----
grails create-taglib format
----

or with your favourite IDE or text editor make a new file with the name `FormatTagLib` in `grails-app/taglib` as given below

[source,groovy]
----
import java.text.SimpleDateFormat

class FormatTagLib {
    def dateFormat = { attrs, body ->
        out << new SimpleDateFormat(attrs.format).format(attrs.value)
    }
}
----

Each Closure property in a tag library that takes one or two arguments is considered a tag. The first argument (typically named `attrs`) will contain the attributes of the tag whilst the optional second argument (typically named `body`) is Closure that represents the inner HTML of the tag declaration from the GSP.

Refer to the user guide topic on link:{guidePath}/theWebLayer.html#taglibs[Tag Libraries] for more information.
