Validation

What Is Validation?

Validation checks a respondent's answers before they can move on. A required question left blank, an email address without a domain, a booking reference in the wrong format, or a departure date that comes before the arrival date is flagged with a message on the question, and the respondent can't go to the next page or complete the form until it's fixed.

Catching mistakes while the respondent is still filling out the form is far cheaper than cleaning up the data afterwards: you receive answers you can use, and respondents get a clear explanation of what to correct instead of a rejected submission or a follow-up email.

In Endatix Hub, you set up validation in the Form Builder without writing code. Mark questions as required, add validation rules — a regular expression, a length or number range, or an expression that compares answers — and write the message respondents see when an answer doesn't pass.

How It Works

• Validation runs when the respondent moves on. By default, answers on a page are checked when the respondent clicks Next or Complete. You can check answers as soon as they're entered instead — see Choosing When Validation Runs.
• A failed check blocks progress. The message appears on the question, the question is highlighted, and the cursor moves to the first invalid answer. The respondent stays on the page until every error is fixed.
• Only "Required" checks empty answers. Every other check — a regular expression, a length, a number range — skips a question that has no answer. An optional question with a format rule accepts a blank answer but rejects a wrong one. The exception is the Expression rule, which runs even when its question is empty.
• Built-in checks run before validation rules. A question's rules are evaluated only after its built-in checks pass: the Required check, the question's minimum and maximum values, an incomplete input mask, and the email format check on an Email input.
• Hidden and read-only questions aren't validated. A question hidden by a condition, or made read-only, never blocks the respondent.
• Not every message is an error. A rule can show a Warning or an Informational note instead — the message is displayed, but the respondent can still continue. See Notification Types.

Example: Validating a Conference Registration Form

A conference registration form collects the attendee's details, a booking reference, travel dates, and workshop choices. Each question uses a different kind of validation.

#	Question type	Question name	Validation
1	Single-Line Input	full_name	Required, with a custom error message
2	Single-Line Input (Input type: Email)	email	Required; email format checked automatically
3	Single-Line Input	booking_reference	Required; Regex rule for the format ABC-1234
4	Single-Line Input (Input type: Number)	attendees	Between 1 and 10, with a custom message above the maximum
5	Single-Line Input (Input type: Date)	arrival_date	Required
6	Single-Line Input (Input type: Date)	departure_date	Required; Expression rule: must be after the arrival date
7	Checkboxes	workshops	No more than two choices
8	Long Text	accessibility_needs	Text rule: at least 20 characters, shown as a Warning

1. Make a Question Required

Select the Full name question on the design surface, then click Required (the asterisk icon) on the question's toolbar. You can also select Required in the Property Grid's General category. A required question shows an asterisk (*) after its title.

Without a custom message, respondents see "Response required." To say what's needed and why, open the Validation category and type your own text in Error message for required questions:

Please enter your full name so we can print your badge.

To require an answer only in certain situations — for example, a company name only when the respondent registers as a business — leave Required cleared and set Make the question required if in the Conditions category instead. See Logic Expressions.

Email inputs check the format for you

When a Single-Line Input's Input type (in the General category) is Email, the question rejects anything that isn't a valid email address, such as jordan.lee@example. You don't need to add a rule for it.

2. Check a Format with a Regular Expression

Booking references always look like ABC-1234: three letters, a hyphen, and four digits. A Regex rule rejects anything else.

1. Select the Booking reference question and open the Validation category.
2. Under Validation rules, click Add new rule (or the + icon). A new Expression rule is added with its settings expanded.
3. Change the rule type from Expression to Regex in the rule's dropdown.
4. In Regular expression, enter ^[A-Z]{3}-\d{4}$.
5. Select Case insensitive so abc-1234 is accepted too.
6. In Notification message for invalid input, explain the expected format:

Enter the reference as three letters, a hyphen, and four digits, for example ABC-1234.

Always write a message for Regex rules

A Regex rule has no default message. Without one, an invalid answer is highlighted in red, but respondents aren't told what's wrong.

See Regular Expressions for pattern syntax and ready-to-use examples.

3. Set a Number Range

A single booking covers between 1 and 10 attendees.

1. Select the Number of attendees question. In the General category, set Input type to Number, Min to 1, and Max to 10.
2. Open the Validation category and replace the text in "Value exceeds maximum" error message with:

Group bookings are limited to {0} attendees.

{0} is replaced with the limit, so respondents who enter 12 read "Group bookings are limited to 10 attendees." The message stays correct if you change Max later.

The same Min and Max settings work for dates and times. Set Max on a Date input to a fixed date, or use Max value expression in the Conditions category — for example, today() — to reject dates in the future.

4. Compare Two Answers with an Expression Rule

The departure date must come after the arrival date. Only an Expression rule can check one answer against another.

1. Select the Departure date question and open the Validation category.
2. Click Add new rule. New rules are Expression rules, so there's no type to change.
3. In Valid when, enter the condition the answer must meet. Type it directly or click the magic wand icon to build it in the condition editor:

{arrival_date} empty or {departure_date} > {arrival_date}

4. In Notification message for invalid input, enter Your departure date must be after your arrival date.

The answer is valid when the expression is true. The {arrival_date} empty or part avoids a misleading message while the arrival date is still blank. See Expression Rules for more examples.

5. Limit the Number of Choices

Attendees can join at most two workshops. Select the Checkboxes question, open Choice Options, and set Maximum choices to select to 2. Once two choices are selected, the remaining ones are disabled until the respondent clears one.

Minimum choices to select works the other way around: selecting too few shows "Please select at least 2 option(s)." when the respondent moves on.

6. Add a Warning Instead of an Error

Short accessibility or dietary notes are often too vague for the venue team, but they shouldn't stop anyone from registering. Select the Long Text question, add a Text rule with Minimum length (in characters) set to 20, write a friendly message, and set Notification type to Warning.

7. Preview the Result

Open the Preview tab, enter some invalid answers, and click Complete. Each question that fails shows its message, and the respondent stays on the page:

When everything looks right, click Save.

Custom Error Messages

Every check has a default message, but a message written for your form tells respondents exactly how to fix their answer. Messages are set in these places:

Check	Where to set the message
Required question	Validation → Error message for required questions
Validation rule	The rule's Notification message for invalid input
Min and Max (Single-Line Input)	Validation → "Value is below minimum" error message and "Value exceeds maximum" error message
Step (Number input)	Validation → "Value does not match step size" error message
Other option left empty	Validation → "Empty comment" error message
Duplicate entries (Dynamic Matrix, Dynamic Panel)	Validation → Error message for duplicate responses

A few things to keep in mind when writing messages:

• Say how to fix the answer, not only that it's wrong. "Enter the reference as three letters, a hyphen, and four digits, for example ABC-1234." beats "Invalid format."
• Use {0} for limits. In the min, max, and step messages, {0} is replaced with the limit that was exceeded.
• Messages can use earlier answers. Placeholders such as {full_name} work in messages the same way they do in titles — see Text Piping.
• Messages are translated with the rest of the form. Custom messages appear in the Translations tab next to the question's title and description. See Form Translation.

Default Messages

Without a custom message, respondents see the default text in the form's language:

Check	Default message (English)
Required	Response required.
Required panel (no question answered)	Response required: answer at least one question.
Email input type, Email rule	Please enter a valid e-mail address.
Min / Max	The value should not be less than {0} / The value should not be greater than {0}
Text rule	Please enter at least {0} character(s). / Please enter no more than {0} character(s).
Text rule with Allow digits cleared	Numbers are not allowed.
Number rule	The 'value' should be at least {0} and at most {1}
Answer count rule, Minimum choices to select	Please select at least {0} option(s).
Expression rule	The expression: {0} should return 'true'. (with the raw expression as {0})
Regex rule	No message
Incomplete input mask	Please complete the value to match the required format.
Other option left empty	Response required: enter another value.
Duplicate entry	This value should be unique.

The Number default doesn't say which value is meant, the Expression default shows respondents the raw expression, and the Regex rule says nothing at all — write your own message for those rules.

Validation Rules

Rules are added in the Validation rules list of a question's Validation category. A question can have several rules; each one that fails shows its own message. A new rule opens with its settings expanded; to edit an existing rule later, click its pencil icon (Show Details). The trash icon removes a rule.

The rule types offered depend on the question type:

Rule	Fails when	Settings	Available for
Expression	The expression in Valid when isn't true	Valid when	Every question type
Text	The answer is shorter or longer than allowed, or contains digits when they aren't allowed	Minimum length (in characters), Maximum length (in characters) (0 = no limit), Allow digits	Long Text; Single-Line Input with Input type Text, Email, Phone Number, Password, or URL
Regex	The answer doesn't match the regular expression	Regular expression, Case insensitive	Same as Text
Email	The answer isn't a valid email address	—	Single-Line Input with Input type Email
Number	The answer isn't a number, or is outside the range	Minimum value, Maximum value	Single-Line Input with Input type Number or Range
Answer count	Too few or too many choices are selected	Minimum count, Maximum count	Checkboxes, Multi-Select Dropdown, Ranking, Image Picker

Every rule also has Notification message for invalid input and Notification type.

Built-in settings or rules?

Several rules overlap with simpler built-in settings: Min and Max instead of a Number rule, the Email input type instead of an Email rule, and Minimum/Maximum choices to select instead of an Answer count rule. Prefer the built-in settings — they also guide the respondent while they answer (for example, by disabling extra choices). Use a rule when you need a Warning or Informational note, or several different messages on the same question.

Notification Types

A rule's Notification type controls how strongly its message is presented:

Notification type	Appearance	Blocks the respondent?	Use it for
Error (default)	Red	Yes	Answers you can't accept
Warning	Orange	No	Answers that are probably a mistake but might be right — an unusually short comment, a very large number
Informational	Blue	No	Neutral guidance — for example, "We'll send your badge to this address."

If a question has messages of several types, only the strongest is shown: warnings appear once all errors are fixed, and informational notes once there are no errors or warnings.

Show warnings as soon as the answer is entered

Because warnings don't block the respondent, a page without errors moves on as soon as Next or Complete is clicked — before the warning can be read. Set the survey's Run validation option to After an answer is changed (see Choosing When Validation Runs) so warnings and notes appear the moment the respondent leaves the field.

Regular Expressions

A Regex rule compares the answer with a regular expression — a pattern that describes which text is allowed. Endatix forms use standard JavaScript regular expression syntax.

Writing a Pattern

• Anchor the pattern with ^ and $. ^ marks the start of the answer and $ the end. Without them, the pattern only has to match somewhere in the answer: \d{4} accepts abc12345xyz because it contains four digits in a row, while ^\d{4}$ accepts exactly four digits.
• Select Case insensitive instead of listing both cases. With it selected, ^[A-Z]{3}$ also accepts abc.
• Type backslashes once in the Property Grid. Enter \d in Regular expression. Only in the JSON Editor is each backslash doubled: "regex": "^\\d{4}$".
• Keep empty answers in mind. A Regex rule doesn't check a blank answer. Select Required as well if the answer is mandatory.

Common Patterns

Allow	Regular expression	Accepts
Exactly six digits (a verification code)	^\d{6}$	048213
US ZIP code, with optional ZIP+4	^\d{5}(-\d{4})?$	94103, 94103-1208
UK postcode (select Case insensitive)	^[A-Z]{1,2}\d[A-Z\d]? ?\d[A-Z]{2}$	SW1A 1AA, m1 1ae
International phone number with country code	^\+[1-9]\d{6,14}$	+442071838750
Letters, spaces, hyphens, and apostrophes only	^[A-Za-zÀ-ÖØ-öø-ÿ' -]+$	Anne-Marie O'Neil
No digits anywhere	^\D*$	Studio B
A web address that starts with https://	^https://\S+$	https://endatix.com
One of a fixed set of codes	^(EU|US|APAC)$	EU, APAC

Test every pattern in the Preview tab with answers that should pass and answers that should fail before you publish the form.

Regex Rules, Input Masks, and regexMatch

• An input mask (Input Mask Settings → Input mask type) shapes the answer while the respondent types — for example, a phone number pattern that inserts the brackets and hyphens. It suits values with a fixed shape. A Regex rule checks the answer afterwards and suits formats with optional or variable parts.
• The regexMatch function tests a pattern inside an expression. Use it in an Expression rule when the pattern should apply only in some cases — see the conditional phone number example below.

Expression Rules

An Expression rule accepts the answer when its Valid when expression is true. Because it can reference any question, variable, or function, it covers checks that no other rule can. The expression syntax is the same one used for conditions — see Logic Expressions for every operator and function.

Check	Question the rule is on	Valid when
The departure date is after the arrival date	departure_date	{arrival_date} empty or {departure_date} > {arrival_date}
Both email addresses match	email_confirm	{email_confirm} = {email}
The respondent is at least 18	date_of_birth	age({date_of_birth}) >= 18
Three percentages add up to 100	budget (Multiple Textboxes)	{budget.marketing} + {budget.sales} + {budget.research} = 100
A UK mobile number format applies only to UK residents	phone	{country} != 'uk' or regexMatch({#phone}, '^(\+44|0)7\d{9}$')

Keep these points in mind:

• Expression rules run even when the question is empty. Write the expression so that a blank answer passes — or select Required — to avoid an error before the respondent has had a chance to answer.
• Put the rule on the question the respondent should fix. The message appears on the question that owns the rule, and that question is the one the cursor moves to.
• Always write a message. The default message shows the raw expression.

Built-in Checks and Limits

Besides required questions and rules, many question types have validation settings of their own.

Single-Line Input and Long Text

Setting	Category	What it does
Input type → Email	General	Rejects values that aren't valid email addresses.
Min, Max	General	Reject values outside the range. Available when Input type is Number, Range, Date, Date and Time, Month, Time, or Week.
Step	General	For Number inputs, rejects values that aren't a multiple of the step — for example, 0.5 with a step of 1.
Min value expression, Max value expression	Conditions	Calculate the limit instead of fixing it — for example, today() to reject future dates.
Input mask type	Input Mask Settings	Formats the answer while typing (Pattern, Numeric, Date and Time, Currency) and rejects an incomplete pattern.
Maximum character limit	Validation	Stops the respondent from typing beyond the limit and shows a character counter. -1 (the default) uses the survey-level Restrict answer length setting in Question Settings; 0 removes the limit.

Choice Questions

Setting	Question types	What it does
Minimum choices to select	Checkboxes, Multi-Select Dropdown	Shows an error when too few choices are selected.
Maximum choices to select	Checkboxes, Multi-Select Dropdown	Disables the remaining choices once the maximum is reached.
"Empty comment" error message	Questions with an Other option	The message shown when Other is selected but its text box is empty — the text box is always required.

Matrices, Panels, and Repeating Questions

Setting	Question types	What it does
Require an answer in each row	Single-Select Matrix	Every row must be answered, not only one.
Prevent duplicate responses in rows	Single-Select Matrix	No two rows can have the same answer.
Required, Prevent duplicate responses, validation rules	Columns of Multi-Select Matrix and Dynamic Matrix	Each column has its own settings, applied to every cell in the column. Cell error message alignment (Layout) sets where cell messages appear.
Minimum row count, Maximum row count	Dynamic Matrix	Limit how many rows the respondent can have.
Prevent duplicate responses in the following column	Dynamic Matrix	Rejects two rows with the same value in the chosen column.
Minimum number of entries, Maximum number of entries	Dynamic Panel	Limit how many entries the respondent can add.
Prevent duplicate responses in the following question	Dynamic Panel	Rejects two entries with the same answer to the chosen question.
Required on a panel	Panel, Dynamic Panel	At least one question inside must be answered.

File Upload

In the General category, Maximum file size (in bytes) rejects larger files — 5242880 allows up to 5 MB — and Accepted file categories limits which kinds of files can be selected.

Choosing When Validation Runs

Survey-wide validation settings are in the survey's own Validation category. Click an empty area of the design surface to show the survey's settings, then open Validation:

Setting	Options
Run validation	When switching to the next page (default) — answers on a page are checked when the respondent clicks Next or Complete. After an answer is changed — each answer is checked as soon as it's entered; for text inputs, when the respondent leaves the field. The respondent sees problems immediately. Upon survey completion — the respondent can move freely between pages; everything is checked when they click Complete, and they are taken back to the first page with an error.
Validate empty fields on lost focus	Available with After an answer is changed. When selected, leaving a required question empty shows its message right away instead of waiting for Next or Complete.
Set focus on the first invalid answer	Selected by default. When validation fails, the cursor moves to the first question with an error.

Related settings in other categories:

• Data → Update input field values — with While typing, text answers are checked as the respondent types rather than when they leave the field (used together with After an answer is changed).
• Question Settings → Error message alignment — shows messages at the Top (default) or Bottom of each question. Override it for a single question in its Layout category, or for all questions in a panel in the panel's Question Settings.
• Question Settings → Required symbol(s) — the marker after required question titles (* by default). See Question Settings.

Important Considerations

• Validation runs in the respondent's browser. It guides respondents filling out the form; answers sent directly to the Endatix API aren't checked against the form's validation settings.
• Editing a submission skips validation. Changes made to a submission from its Submission Details page aren't blocked by the form's rules, so incomplete or out-of-range data can be corrected or kept as needed.
• Hidden questions don't block the respondent. If a question is hidden by a condition, its Required setting and rules are ignored. Use this to require an answer only when a question is relevant.
• Allow digits only rejects answers that end with a digit. With Allow digits cleared, a Text rule rejects Room 12 but accepts 4th floor. To reject digits anywhere, use a Regex rule with ^\D*$.
• Keep regular expressions simple. Patterns with nested repetition, such as (a+)+, can make the form slow to respond on long answers. Anchored patterns with fixed lengths — \d{4} rather than \d+ — are both safer and stricter.
• Choice questions don't offer Text or Regex rules. Those rules check typed answers; to restrict selections, use the limits described in Choice Questions.

Related Documentation

• Logic Expressions — the operators and functions available in Valid when, Make the question required if, and regexMatch.
• Text Piping — insert earlier answers into messages and titles.
• Question Loops — repeat a set of questions for each selected item using Dynamic Panels.
• Form Translation — translate custom error messages with the rest of the form.

Technical Reference (JSON Schema)

The example form looks like this in the JSON Editor:

{
  "title": "Conference Registration",
  "pages": [
    {
      "name": "registration",
      "elements": [
        {
          "type": "text",
          "name": "full_name",
          "title": "Full name",
          "isRequired": true,
          "requiredErrorText": "Please enter your full name so we can print your badge."
        },
        {
          "type": "text",
          "name": "email",
          "title": "Email address",
          "isRequired": true,
          "inputType": "email"
        },
        {
          "type": "text",
          "name": "booking_reference",
          "title": "Booking reference",
          "description": "You'll find it in your confirmation email.",
          "isRequired": true,
          "validators": [
            {
              "type": "regex",
              "text": "Enter the reference as three letters, a hyphen, and four digits, for example ABC-1234.",
              "regex": "^[A-Z]{3}-\\d{4}$",
              "caseInsensitive": true
            }
          ]
        },
        {
          "type": "text",
          "name": "attendees",
          "title": "Number of attendees",
          "inputType": "number",
          "min": 1,
          "max": 10,
          "maxErrorText": "Group bookings are limited to {0} attendees."
        },
        {
          "type": "text",
          "name": "arrival_date",
          "title": "Arrival date",
          "isRequired": true,
          "inputType": "date"
        },
        {
          "type": "text",
          "name": "departure_date",
          "startWithNewLine": false,
          "title": "Departure date",
          "isRequired": true,
          "inputType": "date",
          "validators": [
            {
              "type": "expression",
              "text": "Your departure date must be after your arrival date.",
              "expression": "{arrival_date} empty or {departure_date} > {arrival_date}"
            }
          ]
        },
        {
          "type": "checkbox",
          "name": "workshops",
          "title": "Which workshops will you attend?",
          "description": "Choose up to two.",
          "choices": [
            { "value": "forms_101", "text": "Form design fundamentals" },
            { "value": "logic", "text": "Logic and expressions" },
            { "value": "analytics", "text": "Analytics dashboards" },
            { "value": "integrations", "text": "Webhooks and integrations" }
          ],
          "maxSelectedChoices": 2
        },
        {
          "type": "comment",
          "name": "accessibility_needs",
          "title": "Accessibility or dietary requirements",
          "validators": [
            {
              "type": "text",
              "notificationType": "warning",
              "text": "Could you tell us a bit more? A few details help our venue team prepare.",
              "minLength": 20
            }
          ]
        }
      ]
    }
  ]
}

Question Properties

Property	Type	Applies to	Description
isRequired	boolean	Questions, panels	Required. Default false.
requiredIf	string (expression)	Questions, panels	Make the question required if.
requiredErrorText	string (localizable)	Questions, panels	Error message for required questions.
validators	array	Questions	Validation rules. See Validation Rule Objects.
errorLocation	"default" | "top" | "bottom"	Questions	Error message alignment (Layout). "default" inherits the survey setting.
inputType	string	Single-Line Input (text)	"email" adds the email format check. "number", "range", "date", "datetime-local", "month", "time", and "week" support min and max.
min, max	number | string	Single-Line Input	Min and Max. Dates use the yyyy-mm-dd format.
minValueExpression, maxValueExpression	string (expression)	Single-Line Input	Min value expression and Max value expression, such as today().
minErrorText, maxErrorText, stepErrorText	string (localizable)	Single-Line Input	Messages for values below min, above max, or off step. {0} is replaced with the limit.
step	number	Single-Line Input (inputType: "number")	Step.
maxLength	number	Single-Line Input, Long Text (comment)	Maximum character limit. -1 (default) uses the survey's maxTextLength; 0 means no limit.
minSelectedChoices, maxSelectedChoices	number	Checkboxes (checkbox), Multi-Select Dropdown (tagbox)	Minimum choices to select and Maximum choices to select. 0 means no limit.
otherErrorText	string (localizable)	Choice questions	"Empty comment" error message.
eachRowRequired, eachRowUnique	boolean	Single-Select Matrix (matrix)	Require an answer in each row and Prevent duplicate responses in rows.
keyName	string	Dynamic Matrix (matrixdynamic), Dynamic Panel (paneldynamic)	The column or question whose value must be unique across rows or entries.
keyDuplicationError	string (localizable)	Dynamic Matrix, Dynamic Panel	Error message for duplicate responses.
columns[].isRequired, columns[].isUnique, columns[].validators	boolean, boolean, array	Multi-Select Matrix (matrixdropdown), Dynamic Matrix	Required, unique-value, and rule settings for every cell in a column.
items[].isRequired, items[].validators	boolean, array	Multiple Textboxes (multipletext)	Required and rule settings for an individual textbox.
minRowCount, maxRowCount	number	Dynamic Matrix	Minimum row count and Maximum row count.
minPanelCount, maxPanelCount	number	Dynamic Panel	Minimum number of entries and Maximum number of entries.
maxSize	number	File Upload (file)	Maximum file size (in bytes). 0 means no limit.

Validation Rule Objects

Each entry in validators has a type and the properties for that type. All rules share text and notificationType.

type	Property Grid name	Properties
(all)	—	text (string, localizable) — Notification message for invalid input. notificationType ("error" | "warning" | "info", default "error") — Notification type.
"expression"	Expression	expression (string) — Valid when.
"text"	Text	minLength, maxLength (number, default 0 = no limit); allowDigits (boolean, default true).
"regex"	Regex	regex (string) — escape each backslash in JSON: "^\\d{4}$"; caseInsensitive (boolean, default false).
"email"	Email	—
"numeric"	Number	minValue, maxValue (number).
"answercount"	Answer count	minCount, maxCount (number).

Survey Properties

Property	Type	Default	Description
checkErrorsMode	"onNextPage" | "onValueChanged" | "onComplete"	"onNextPage"	Run validation.
validateVisitedEmptyFields	boolean	false	Validate empty fields on lost focus. Applies when checkErrorsMode is "onValueChanged".
autoFocusFirstError	boolean	true	Set focus on the first invalid answer.
textUpdateMode	"onBlur" | "onTyping"	"onBlur"	Update input field values.
questionErrorLocation	"top" | "bottom"	"top"	Error message alignment.
requiredMark	string	"*"	Required symbol(s).
maxTextLength, maxCommentLength	number	0	Restrict answer length — the default maxLength for Single-Line Input and Long Text questions — and Restrict comment length — the limit for comment boxes and Other text boxes. 0 means no limit.

Example — Warning and Informational Notes with Immediate Validation

{
  "checkErrorsMode": "onValueChanged",
  "pages": [
    {
      "name": "page1",
      "elements": [
        {
          "type": "text",
          "name": "attendees",
          "title": "Number of attendees",
          "inputType": "number",
          "min": 1,
          "validators": [
            {
              "type": "numeric",
              "maxValue": 50,
              "notificationType": "warning",
              "text": "That's a large group. Please double-check the number before you continue."
            }
          ]
        },
        {
          "type": "text",
          "name": "email",
          "title": "Email address",
          "inputType": "email",
          "isRequired": true,
          "validators": [
            {
              "type": "expression",
              "expression": "{email} notempty",
              "notificationType": "info",
              "text": "We'll send your badge and invoice to this address."
            }
          ]
        }
      ]
    }
  ]
}

Example — Conditional Pattern with regexMatch

A UK mobile number is required to match its format only when the respondent lives in the UK:

{
  "type": "text",
  "name": "phone",
  "title": "Mobile number",
  "inputType": "tel",
  "validators": [
    {
      "type": "expression",
      "expression": "{country} != 'uk' or regexMatch({#phone}, '^(\\+44|0)7\\d{9}$')",
      "text": "Enter a UK mobile number without spaces, for example 07700900123."
    }
  ]
}