"Placeholder" attribute for text-based inputs

I noticed the `textarea` widget has a `placeholder` attribute for showing some text before any text is actually input (using the HTML `placeholder` input attribute). Can this functionality be extended to other text-based inputs (`fields.string`, `fields.email`, `fields.password`, `fields.number`) as well? For example:

Full_Name: fields.string({
errorAfterField: true,
placeholder: "Please enter your full name.",
required: validators.required("Please enter your full name."),
validators: [
validators.maxlength(50)
]
}),

produces: