In some cases, we need to enter a limited character variable. For such cases, we can limit the sequencer Form block with the Regular expression which is a sequence of characters that define a search pattern. You can create and re-check the expression in any of the online testers, one of them is Regular expression 101.
When the Form block is added, it needs to be adjusted as an input. With the click on the three-dotted button, the additional settings will open.
On the bottom, there is an input field where we can enter the Regular expression syntax.
Example: We need to enter a string with 6 characters, which can be case sensitive letters or a number.
The following expression allows us to enter any digit from 0-9 (\d), any character in the range of a-z and also big caption letters in the range from A-Z. The additional parameter {6} defines the exact number of the characters.
^[\da-zA-Z]{6}$
If the entered characters don't match the wanted condition (Regular expression) the input box turns Red. If you press the OK button in this state the software will output the Validation error and the Sequence will not continue.
When you enter a valid expression the input box turns white and you can normally continue with the sequence.