When CGI ruled the Web, CGI::FormBuilder was one of the good ways of keeping the form DRY by having the same code generate the form and validate passed parameters once it is submitted.

I am writing a small Dancer2 web application which needs to have a form. Originally I had considered generating and validating the form from the same description, but then I realised that such generated form would be limited in terms of layout I want to present to the user. For example, most of the fields follow a simple template: 

<p>
    <label for="[% id %]">[% name %] = </label>
    <input
        name="[% id %]" placeholder="[% placeholder %]" type="text"
        id="[% id %]" [% required %] pattern="[% regex %]"
    >
    <label for="[% id %]">[% units %]</label>
</p>

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But a few fields are more complicated, for example, there is two fields per one item description: 
<p>
    <label for="lowwl">Wavelength:</label>
    <input
        name="lowwl" placeholder="400" type="text" id="lowwl"
        pattern="(\d+\.?\d*|\.\d+)([eE][+-]?\d+)?"
    >
    <label> - </label>
    <input
        name="upwl" placeholder="600" type="text" id="upwl"
        pattern="(\d+\.?\d*|\.\d+)([eE][+-]?\d+)?"
    >
    <label for="upwl">nm</label>
</p>

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What are the best practices for form design in 2019? Should I generate the form? (if so, how should I structure the form description if I have to account for various deviations from the template?) Should I keep the form and the form code separate, but complain loudly in case I receive an unexpected parameter? (my original goal in pursuing DRY is preventing typos and facilitating later updates)

In reply to Form generation and validation by Anonymous Monk

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