Sound change rules (also known as phonological rules) are mainly used in the Sound Change field and in custom affixes. This notation can also be used in the Custom Spelling field to mimic spelling idiosyncrasies of natural languages, and in illegal combinations field to prohibit combinations of phonemes.

A basic rule like a > e changes every a to e. Try it yourself:

You can also specify if the change should only happen in a particular environment: a > e / _b changes every a to e if it comes before a b. The / means "in the environment of" and _ signifies where the a is.

Word boundary

# signifies a word boundary. Notice how the following pattern only changes the first a.

Multiple symbols

You can capture multiple symbols inside curly brackets, eg {b,m}:

Shorthand symbols

Vulgar uses various shorthand abbreviations for classes of phonemes, such as C for "any consonant" or V for "any vowel":

Here is a complete list:

Quantifiers

A question mark ? makes anything before it optional:

Use round brackets to capture a longer pattern:

Plus symbol + means one or more of whatever is before it:

Star symbol * means zero or more of whatever is before it:

Backreferences

Numbers refer back to whatever was captured inside brackets. The number 1 refers to whatever was matched in the first brackets. The following pattern matches a vowel at the end of the word, and doubles it:

The following pattern matches two consonants in a row and swaps them:

Zero refers to the entire match:

Null symbol

Note: Ø signifies nothing (not to be confused with zero!).

Exceptions to rules

The ! symbol signifies an exception to a rule: m > n / !_e changes m to n except before e. Similarly, m > n / !e_ changes m to n except after e (this may not work in older browsers).

Exception rules can also be added to the end of a normal rule, eg: m > n / _e !s_ means m changes n before e, except after s.

Reduplication

The dot symbol . matches any character. You can combine some rules we have already learned to reduplicate an entire match:

Dealing with stress symbols

If you want to make spelling rules that are sensitive to stress, you first need to check the Make spelling rules sensitive to stress symbol option. (The default setting is to apply the spelling rules with the stress symbol already removed, so that you don't have to worry about the stress symbol making your patterns more complicated.) Let's say you want stressed a to turn into á, like in Spanish spelling. The stress symbol could come right before an a, as in ˈama, however it could also come before any number of consonants and then an a, as in ˈdrama. To capture zero or more consonants you need to write C*. And don't forget about the stress symbol!.

Finally, you will need a second rule to replace stress symbols with nothing.

Non-Latin alphabets

Custom spelling supports all Unicode alphabets and scripts, such as Japanese, Chinese, Cyrillic, Georgian and even Unicode Emojis.

Order of rules

The order of your custom spelling rules matter. Vulgar will find-and-replace the first spelling rule to a word, then apply the next rule over the top of what it just did. This can be a problem if a IPA symbol appears in multiple patterns. For instance, the following rules are problematic:

ʊ > u
aʊ > ow

The intent here is for the diphthong aʊ (as in the word "cow") to change to ow. However, a previous rule has already changed any ʊ (as in the word "put") to u, which means aʊ has already changed to au. The easiest solution is to reverse the order of the rules:

aʊ > ow
ʊ > u

Another solution is to use the ! symbol to add an "except when" condition: ʊ > u / !a_.