Constraint

The constraint column is used to validate user input. It prevents the user from continuing until the answer meets a condition you define.

If the answer doesn't satisfy the constraint, a message defined in constraint_message is shown to the user.

📝 How constraints work

The value of the question is represented by a dot (.), which means “the current answer.” You build a logic expression using that value.

Constraints are commonly used to:

• Set numeric ranges (e.g., age must be between 0 and 120)

• Require matching formats (e.g., ZIP codes, emails)

• Enforce dependencies (e.g., end date after start date)

type	name	label	constraint	constraint_message
integer	age	Your age	. >= 18 and . <= 99	Age must be between 18 and 99
text	zip	ZIP code	regex(., '^\d{5}$')	Enter a 5-digit ZIP code
text	email	Email address	regex(., '^[^@]+@[^@]+.[^@]+$')	Enter a valid email
date	end	End date	. >= ${start}	End date must be after start

☑️ Using the dot (.) in constraint

The dot . represents the value entered by the user for the current question. Use it inside functions and expressions:

• . >= 0 — valid if value is 0 or higher

• regex(., '^\d{5}$') — valid if it matches the pattern

🔠 Variable references

You can use ${question_name} to reference answers from other questions in the form. Make sure referenced questions appear earlier in the form.

Example:

• . > ${min_age} — ensures current input is greater than a previously entered value

🔢 Operators and functions for constraints

Same as relevance, you can use:

=, !=, >, <, >=, <= and, or, not()

Function	Description	Example
regex()	Validates the format of a text input	regex(., '^\d{5}$') for US ZIP codes
string-length()	Checks the number of characters	string-length(.) <= 50
selected()	Checks if a choice was selected	selected(${choices}, 'option1')
today()	Gets the current date	. <= today()
now()	Gets current date and time	. <= now()