# phpman > perldoc > Font::TTF::Coverage

## NAME
    [Font::TTF::Coverage](https://www.chedong.com/phpMan.php/perldoc/Font%3A%3ATTF%3A%3ACoverage/markdown) - Opentype coverage and class definition objects

## DESCRIPTION
    Coverage tables and class definition objects are virtually identical concepts in OpenType. Their
    difference comes purely in their storage. Therefore we can say that a coverage table is a class
    definition in which the class definition for each glyph is the corresponding index in the
    coverage table. The resulting data structure is that a Coverage table has the following fields:

    cover
        A boolean to indicate whether this table is a coverage table (TRUE) or a class definition
        (FALSE)

    val A hash of glyph ids against values (either coverage index or class value)

    fmt The storage format used is given here, but is recalculated when the table is written out.

    count
        A count of the elements in a coverage table for use with add. Each subsequent addition is
        added with the current count and increments the count.

    max Maximum class value in a class table.

## METHODS
  new($isCover [, vals])
    Creates a new coverage table or class definition table, depending upon the value of $isCover. if
    $isCover then vals may be a list of glyphs to include in order. If no $isCover, then vals is a
    hash of glyphs against class values.

  read($fh)
    Reads the coverage/class table from the given file handle

  out($fh, $state)
    Writes the coverage/class table to the given file handle. If $state is 1 then the output string
    is returned rather than being output to a filehandle.

  $c->add($glyphid[, $class])
    Adds a glyph id to the coverage or class table. Returns the index or class number of the glyphid
    added.

  $c->signature
    Returns a vector of all the glyph ids covered by this coverage table or class

  @map=$c->sort
    Sorts the coverage table so that indexes are in ascending order of glyphid. Returns a map such
    that $map[$new_index]=$old_index.

  $c->out_xml($context)
    Outputs this coverage/class in XML

## AUTHOR
    Martin Hosken <<http://scripts.sil.org/FontUtils>>.

## LICENSING
    Copyright (c) 1998-2016, SIL International (<http://www.sil.org>)

    This module is released under the terms of the Artistic License 2.0. For details, see the full
    text of the license in the file LICENSE.