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I am trying to implement HTML5 validation from https://docs.cypress.io/faq/questions/using-cypress-faq#Can-I-check-that-a-forms-HTML-form-validation-is-shown-when-an-input-is-invalid but when I use this code snippet, 

sourceAccount().then(input => {
                expect(input[0].validationMessage).to.equal('Please select an item in the list.');
            })

validationMessage variable is not recognised. What could be the reason?  I am using Cypress 12.12.0