> For the complete documentation index, see [llms.txt](https://support.docstudio.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://support.docstudio.com/user/template-builder/template-dynamic-fields/field-masks-regex.md).
# Field masks (RegEx)
**Field masks, also known as regular expressions (RegEx)**, are powerful tools used for validating and processing text. They help ensure the accuracy of user input, such as postal codes, email addresses, USREOU codes, phone numbers, and more.\
\
Field masks consist of sequences of characters, some of which have special meanings (known as metacharacters) that allow for complex validation conditions.
DocStudio not only provides a list of pre-made standard masks for validating user input but also allows users to create custom masks tailored to specific business processes.
{% columns %}
{% column %}
You can enable mask settings both when adding new fields to a template and when editing existing fields in a created template.
To do this, use the **Mask** option in the properties of the field you are configuring:
From the drop-down list, you can choose from **standard mask** options or **Custom** option to **create your own**.
{% endcolumn %}
{% column %}
{% endcolumn %}
{% endcolumns %}
### What standard masks are available for use?
| Standart masks |
| -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
|
Taxpayer Identification Number Checks: 10-digit identification code of an individual. RegEx: ^\d{10}$ ✅ Examples: 1234567890 ❌ Invalid: 123456789 (9 digits), 12345678901 (11 digits)
|
|
Email Address Checks: Email address in standard format. RegEx: ^\[a-zA-Z0-9.\_%+-]+@\[a-zA-Z0-9.-]+.\[a-zA-Z]{2,}$ ✅ Examples: , ❌ Invalid: , user\@domain, user\@domain..com
|
|
Bank Account (IBAN) Checks: IBAN (International bank account number). RegEx: ^\[A-Z]{2}\d{2}\[A-Z\d]{11,30}$ ✅ Examples: UA123456789012345678901234567 ❌ Invalid: UA12ABC, 12345678
|
|
Credit Card Number Checks: 16-digit credit card number (no spaces). RegEx: ^\d{16}$ ✅ Examples: 1234567812345678 ❌ Invalid: 1234 5678 1234 5678, 12345678
|
Summary Table: , , and
| IPN | `^\d{10}$` | 10 digits |
| --------------- | -------------------------------------------------- | -------------------------- |
| Phone | `^\+380\d{9}$` | +380 + 9 digits |
| Email | `^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$` | Standart email |
| Index | `^\d{5}$` | 5 digits |
| Passport | `^[А-ЯЄІЇ]{2}\d{6}$` | 2 letters + 6 digits |
| IBAN | `^[A-Z]{2}\d{2}[A-Z\d]{11,30}$` | International bank account |
| Card number | `^\d{16}$` | 16 digits |
| GTIN | `^(\d{8}\|\d{12}\|\d{13}\|\d{14})$` | 8, 12, 13 or 14 digits |
| GLN | `^\d{13}$` | 13 digits |
| Product Article | `^[A-Z0-9-]{5,10}$` | 5 to 10 symbols |
| MFO | `^\d{6}$` | 6 digits |
### How to Create Custom Masks?
As mentioned, field masks are based on regular expressions, so you'll need to create your own expression.
Before you begin, clearly define the **valid** and **invalid** values.
A regular expression consists of special characters (metacharacters) that establish the validation rules.
Here’s a **compact reference table** to assist you in creating regular expressions.\
It includes the main symbols, their descriptions, and examples of their usage.
| **Symbol** | **Description** | **Example** |
| ---------- | ----------------------------------------- | -------------------------- |
| `^` | Start of line | `^a` → "abc", not "ba" |
| `$` | End of line | `a$` → "ba", not "ab" |
| `\d` | Any number (0-9) | `\d` → "5", "9" |
| `\D` | Not a number | `\D` → "a", "#" |
| `\w` | Any letter, number or \_ | `\w` → "a", "1", "\_" |
| `\W` | Not a letter, not a number, not a \_ | `\W` → "@", " " |
| `[A-ZА-Я]` | Any capital Latin or Cyrillic letter | `[A-ZА-Я]` → "A", "Я", "B" |
| `{n}` | Repeat exactly 'n' times | `a{2}` → "aa" |
| `{n,}` | 'n' or more repetitions | `a{2,}` → "aa", "aaa" |
| `{n,m}` | From 'n 'to 'm' repetitions | `a{1,3}` → "a", "aaa" |
| `[abc]` | Any character from the set | `[abc]` → "a", "b", "c" |
| `[0-9]` | Any number | `[0-9]` → "5", "9" |
| `[^abc]` | Any character other than from the set | `[^abc]` → "d", "1" |
| `[a-z]` | Character range | `[a-z]` → "b", "k" |
| `\|` | The logical alternative condition is ‘or’ | `a\|b` → "a", or "b" |
| `.` | Any character other than a newline | `a.c` → "abc", "a1c" |
| `*` | 0 or more repetitions | `a*` → "", "a", "aaa" |
| `+` | 1 or more repetitions | `a+` → "a", "aaa" |
| `?` | 0 or 1 repetition | `a?` → "", "a" |
| `\s` | Space character | `\s` → " ", "\t" |
| `\S` | Non-space character | `\S` → "a", "1" |
| `( )` | Grouping | `(ab)+` → "ab", "abab" |
#### **Creating a Regular Expression Example**
Let’s consider the Tax Identification Number (IPN) of a legal entity, which consists of 12 digits (not 10). The regular expression to validate this is: `^\d{12}$`
Let's analyse it:
* `^` — Indicates the beginning of the line
* `\d{12}` — Represents exactly **12 digits**
* `$` — Indicates the end of the string
✅ **Examples**: 123456789012 — Valid\
❌ **Invalid**: 1234567890 — Not valid (contains only 10 digits)
#### **Testing Regular Expressions**
Before using the created expressions, it's recommended to test them.\
Special tools can help with this.
For example, [regex101.com](https://regex101.com/) is a powerful and user-friendly online tool for creating, testing, and analysing regular expressions
* **Interactive Online Testing**:\
Enter your regular expression in the upper field. Input test strings in the field below. The matching results will be displayed instantly.
* **Every symbol explanation**:\
In the right pane (labelled ‘Explanation’), the site explains each character or element of your regular expression.
#### **Popular Custom Masks (RegEx)**
For your convenience, here’s a list of ready-made custom masks that may be useful for validating various popular documents:
Document Name
Mask (RegEx)
IPN of a legal entity (12 digits)
^\d{12}$
IPN (10 digits) or passport (ID card, 9 digits)
^(\d{10}|\d{9})$
Biometric passport (ID card) 9 digits
^\d{9}$
Passport with 2 letters + 6 digits or ID card 9 digits
^[А-ЯЄІЇ]{2}\d{6}|\d{9})$
Passport in booklet form 2 letters + 6 digits or IPN 10 digits
^([А-ЯЄІЇ]{2}\d{6}|\d{10})$
Passport in booklet form 2 letters + 6 digits or IPN 10 digits or ID card 9 digits