inc/class-Iac_Settings.php
public function checkbox( $attr ) {

		$id      = $attr[ 'label_for' ];
		$name    = $attr[ 'name' ];
		$current = $this->options[ $id ];
		?>
		<input
			type="checkbox"
			name="<?php echo $name; ?>"
			id="<?php echo $attr[ 'label_for' ]; ?>"
			value="1"
			<?php checked( $current, '1' ); ?>
		/>
		<?php
		if ( ! empty( $attr[ 'description' ] ) ) { ?>
			<p class="description"><?php echo $attr[ 'description' ]; ?></p>
			<?php
		}
	}
public function checkbox( $attr ) {

		$id      = $attr[ 'label_for' ];
		$name    = $attr[ 'name' ];
		$current = $this->options[ $id ];
		?>
		<input
			type="checkbox"
			name="<?php echo $name; ?>"
			id="<?php echo $attr[ 'label_for' ]; ?>"
			value="1"
			<?php checked( $current, '1' ); ?>
		/>
		<?php
		if ( ! empty( $attr[ 'description' ] ) ) { ?>
			<p class="description"><?php echo $attr[ 'description' ]; ?></p>
			<?php
		}
	}
prints the form field

@param array $attr
@return void