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  civitatem     Z => 'bdg'              cidade
  adoptare                              adotar
  opera         Rules                   obra
  secundus                              segundo
                s//_#
                m//_#
                e//Vr_#
                v//V_V
                u/o/_#
                gn/nh/_
                S/Z/V_V
                c/i/F_t
                c/u/B_t
                p//V_t
                ii/i/_
                e//C_rV

=head3 Format of sound change rules

Hopefully, the format of the rules will be familiar to any linguist.
For instance, here's one sound change:

  c/g/V_V

This rule says to change C<c> to C<g> between vowels. (We'll see how
to generalize this rule below.)

More generally, a sound change looks like this:

  x/y/z

where C<x> is the thing to be changed, C<y> is what it changes to,
and C<z> is the environment.

The C<z> part must always contain an underline C<_>, representing the
part that changes. That can be all there is, as in

  gn/nh/_

which tells the module to replace C<gn> with C<nh> unconditionally.

The character C<#> represents the B<beginning or end> of the word. So

  u/o/_#

means to replace C<u> with C<o>, but only at the end of the word.

The middle (C<y>) part can be B<blank>, as in

  s//_#

This means that C<s> is B<deleted> when it ends a word.

=head3 Variables

The evironment (the C<z> part) can contain B<variables>, like C<V>
above. These are defined in the first parameter to the constructor.
I use capital letters for this, though this is not a requirement.
Variables can only be one character long. You can defined any variables
needed to state your sound changed. E.g. you could define C<S> to be
any stop, or C<K> for any coronal, or whatever.

So the variable definition and rule

  F => 'ie'

  c/i/F_t

means that C<c> changes to C<i> after a front vowel and before a C<t>.

You can use variables in the first two parts as well. For instance,
suppose you've defined

  S => 'ptc',
  Z => 'bdg'

  S/Z/V_V

This means that the stops C<ptc> change to their voiced equivalents
C<bdg> between vowels. In this usage, the variables must correspond
one for one--C<p> goes to C<b>, C<t> goes to C<d>, etc. Each character
in the replacement variable (here C<Z>) gives the transformed value
of each character in the input variable (here C<S>). Make sure the two
variable definitions are the same length!

A variable can also be set to a fixed value, or deleted. E.g.

  Z//V_V

says to delete voiced stops between vowels, and

  Z/?/V_V

would translate all voiced stops between vowels to a glottal stop C<?>.

=head3 Rule order

Rules apply in the B<order> they're listed. So, with the word C<opera>
and the rules

  p/b/V_V
  e//C_rV

the first rule voices the C<p>, resulting in C<obera>; the second
deletes an C<e> between a consonant and an intervocalic C<r>, resulting
in C<obra>.

The C<printRules> option can assist in debugging rules, since it causes
the output to show exactly what rules applied to each word.

=head3 Optional elements in the environment

One or more elements in the environment can be marked as B<optional>
with parentheses. E.g.

  u/ü/_C(C)F

says to change C<u> to C<ü> when it's followed by one or two
consonants and then a front vowel.

=head2 How to use it