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JavaScript client validation is not available for visitor validations.
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Because client side validation does not talk to the server, the theme (xhtml theme or css_xhtml theme) is responsible for properly manipulating the HTML DOM to display the error message inline. The JavaScript that is responsible for doing this logic is validation.js and can be found in each theme.
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Errors are reported using the default validation message, not the internationalized version that the server-side might be aware of. This is a known issue. You may want to try the AJAX Client Side Validation for messages that are fully internationalized.
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Additional Validator Support
If you wish to add additional validator support beyond those listed, you may override the xhtml theme teamplte form-close-validate.ftl. This file contains the JavaScript that tries to validate each user-entered value from within the browswer. The css_xhtml theme extends the xhtml theme and therefore doesn't have it's own form-close-validate.ftl template.