# Class AlphabetExpansion
Modifier that adds a character to an alphabet.

Defined in | <seqan/modifier.h>
Signature | `template <typename TAlphabet, char CHAR[, typename TSpec]> class ModifiedAlphabet<TAlphabet, ModExpand<CHAR,TSpec> >;`

## Template Parameters

`TAlphabet` | Original value type.
`CHAR` | `char` character that specifies, what value should added to the alphabet. `CHAR` should not be a `char` that already stands for a value in `TAlphabet`. For example, do not use `'A'` or `'a'` as `CHAR` when expanding Dna.
`TSpec` | Optional specialization tag. This modifier is intended to expand SimpleType classes, default is `Default`.

## Detailed Description

### Special Characters

Some values of `CHAR` have special meaning:

`'-'`
  A gap character. The value in the expanded alphabet that corresponds to `'-'` will be returned by the function gapValue.
`'$'`
  An end of string character.

#### Dox Sources

    /*!
     * @class AlphabetExpansion
     *
     * @headerfile <seqan/modifier.h>
     *
     * @brief Modifier that adds a character to an alphabet.
     *
     * @signature template <typename TAlphabet, char CHAR[, typename TSpec]> class
     *            ModifiedAlphabet<TAlphabet, ModExpand<CHAR,TSpec> >;
     *
     * @tparam TAlphabet Original value type.
     * @tparam CHAR <tt>char</tt> character that specifies, what value should added
     *              to the alphabet. <tt>CHAR</tt> should not be a <tt>char</tt>
     *              that already stands for a value in <tt>TAlphabet</tt>. For
     *              example, do not use <tt>'A'</tt> or <tt>'a'</tt> as
     *              <tt>CHAR</tt> when expanding Dna.
     * @tparam TSpec Optional specialization tag. This modifier is intended to
     *               expand SimpleType classes, default is <tt>Default</tt>.
     *
     * @section Special Characters
     *
     * Some values of <tt>CHAR</tt> have special meaning:
     *
     * <dl> <dt><tt>'-'</tt></dt> <dd>A gap character. The value in the expanded
     * alphabet that corresponds to <tt>'-'</tt> will be returned by the function
     * gapValue.</dd> <dt><tt>'$'</tt></dt> <dd>An end of string character.</dd>
     * </dl>
     */