code/dataobjects/FusionTag.php
public function validate() {

		$result = parent::validate();
		$this->Title = strtolower($this->Title);
		if($result->valid() && !$this->Title) {
			$result->error('"Title" required!');
		}
		else if($result->valid() && FusionTag::get_one('FusionTag', array(
			'ID != ?' => $this->ID,
			'Title = ?' => $this->Title
		))) {
			$result->error('Tag already exists!');
		}

		// Allow extension.

		$this->extend('validateFusionTag', $result);
		return $result;
	}
public function validate() {

		$result = parent::validate();
		$this->Title = strtolower($this->Title);
		if($result->valid() && !$this->Title) {
			$result->error('"Title" required!');
		}
		else if($result->valid() && FusionTag::get_one('FusionTag', array(
			'ID != ?' => $this->ID,
			'Title = ?' => $this->Title
		))) {
			$result->error('Tag already exists!');
		}

		// Allow extension.

		$this->extend('validateFusionTag', $result);
		return $result;
	}
Confirm that the fusion tag has been given a title and doesn't already exist.