Source

File: wp-includes/class-wp-object-cache.php

public function incr( $key, $offset = 1, $group = 'default' ) {
		if ( empty( $group ) ) {
			$group = 'default';
		}

		if ( $this->multisite && ! isset( $this->global_groups[ $group ] ) ) {
			$key = $this->blog_prefix . $key;
		}

		if ( ! $this->_exists( $key, $group ) ) {
			return false;
		}

		if ( ! is_numeric( $this->cache[ $group ][ $key ] ) ) {
			$this->cache[ $group ][ $key ] = 0;
		}

		$offset = (int) $offset;

		$this->cache[ $group ][ $key ] += $offset;

		if ( $this->cache[ $group ][ $key ] < 0 ) {
			$this->cache[ $group ][ $key ] = 0;
		}

		return $this->cache[ $group ][ $key ];
	}