To use this functionality edit your tracker field type and got to the Validation section.
Enter the validation type you want to apply to the value entered, the parameters that are necessary and the error message if the validation fails.

You can use a regex Expression to compare the entered value and the expected string.

Validate email address

For parameters you can enter the following (without start and end backslash)

^[ '\-_a-zA-Z0-9@\.]*$

It works perfectly with fields that take text input but is not really suited or relevant to fields that have pre-configured selections, etc. (drop downs).

The Validation feature, under jQuery plugins and add-ons settings in the Features → Interface panel has to be enabled for this to work.

When editing or adding a tracker field while configuring a tracker, you can choose a validation option:

• captcha: Checks if the input text matches an antibot-captcha.
• distinct: Checks if the input text has been used before in the tracker for this field - thus ensuring all tracker items can be unique with respect to the validated field
• pagename: Checks if the input text matches an existing page name
• username: Checks if username has been used already and is valid according to the rules configured in Tiki
• password: Checks if the password is valid according to the rules configured in Tiki
• regex: checks the entered text against any perl regular expression. Enter the regular expression as the "Validation parameter". (Do not include the starting and ending "/" enclosing the regular expression. These will be added automatically.)

Not all validation methods require a "Validation parameter" to be set.

Regardless of which validation method is selected, you can specify a default custom error message if desired, in "Validation error message:"

Click to expand

Developers can add new custom validation procedures in lib/validators. Each validator must be stored in a php file named "validator_nameofvalidator.php" and there must be a main function in the file with the general structure as follows:

function validator_nameofvalidator($input, $parameter = '', $message = '') {
  …
  …
  …
  if ($error) {
      return tra($message); // error message to be shown
  }

  return true; // successful validation
}

It is also necessary to add a line in file lib/core/Services/Tracker/Controller.php in the list of all validators

'regex' => tr('Regular Expression (Pattern)'),
               'username' => tr('User Name'),
               'nameofvalidator' => tr('My Validator I Wrote by Myself'),

$parameter will be what is configured as the "Validation parameter:" in the tracker field settings, and $message is what is configured as the "Validation error message:" in the tracker field settings. You don't have to return $message as the error message if you don't want to (you can return any error message you want depending on the type of the error it is).

It is possible to add custom validation in a wiki page which contains a Tracker plugin through jQuery. If the jQuery validation fails, it should set:
nosubmitItemForm1 = true;
for the first tracker plugin, nosubmitItemForm2 for the second, etc.
It is necessary that this jQuery plugin is above the Tracker plugin.

Example validation for a field of type "ins_fill" (Multiple Fill Fields available) which should start with a number:

{JQ()}
nosubmitItemForm1 = false;
$('#editItemForm1').submit(function() {
        //alert('départ');
        var valeurs = $('#ins_fill').val();
        //alert('valeurs ' + valeurs);
        var listeValeurs = valeurs.split("\n");
        var $errorCount = 0;
        var $errorDots = ""; // build a vertical string for pointing lines in error (optional)
        var $validPattern = /(^\s*\d+\s*,)|(^\s*$)/; // this pattern ensures the first item is a number (comma separated fields)
        for (var i in listeValeurs) {
            //alert(listeValeurs[i]);
            if ( listeValeurs[i].search($validPattern) != -1 ) {
                //alert("'"+listeValeurs[i]+"' est valide");
                $errorDots += "
";
            } else {
                $errorCount++;
                $errorDots += "× 
";
            }
        }
        $('#errorfill').remove();
        $('label.errorspiral').remove(); // Let's not interfere with the error class which is controlled by jquery's validation feature
        $('#ins_fill').removeClass('errorspiral').css({'width':'99%'});
        if( $errorCount == 0 ) { // C'est bon
                //alert('good');
                nosubmitItemForm1 = false;
        } else {
                nosubmitItemForm1 = true;
                $('#ins_fill').before($errorDots+"").css({'width':'90%'}).addClass('errorspiral');
                $('#errorfill').css({'float':'left'});
                alert("ERREUR" + "\n" + "La bonne syntaxe est : nombre,critère"+"\n"+"Nombre de lignes fautives : " + $errorCount);
        }
        if ( valeurs == '' ) { // Do our own detection of required field so we can have translated messages
                nosubmitItemForm1 = true;
                $('#ins_fill').addClass('errorspiral').after('' + tr('This field is required') + '');
                nosubmitItemForm1 = true;
        }
        return false;
});{JQ}