Clear cache tag

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## Overview
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INTRODUCTION
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What?

A cache tag is a string.

Cache tags are passed around in sets (order doesn't matter) of strings, so they are type hinted to string[]. They're sets because a single cache item can depend on (be invalidated by) many cache tags.

Syntax
By convention, they are of the form thing: identifier — and when there's no concept of multiple instances of a thing, it is of the form thing. The only rule is that it cannot contain spaces.

There is no strict syntax.

Examples:

node:5 — cache tag for Node entity 5 (invalidated whenever it changes)
user:3 — cache tag for User entity 3 (invalidated whenever it changes)
node_list — list cache tag for Node entities (invalidated whenever any Node entity is updated, deleted or created, i.e. when a listing of nodes may need to change). Applicable to any entity type in following format: {entity_type}_list.
config:system.performance — cache tag for the system.performance configuration
library_info — cache tag for asset libraries
my_custom_tag - Your Custom tag

INSTALLATION
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* Install, as usual, see http://drupal.org/node/895232 for further information.

CONFIGURATION
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* Configure user permissions in Administration » People » Permissions:

HOW TO USE:
This module allows admin users to clear cache tag.

1. Goto Configuration > Development > Clear cache tag
2. Enter cache tags (custom/core) separated by a comma.
3. Click on the submit button to invalidate.
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* Access menu from here : admin/config/development/clear-cache-tag