title: Validation for non-negative integers and decimal values
body: <p>My fields are:
  <code>tax rate</code> and <code>tax amount</code> in which I want to validate positive values.</p>
  
  <p>I wrote this validation:</p>
  
  <pre><code>:format =&gt; { :with =&gt; /\A[+]?\d+\Z/}
  </code></pre>
  
  <p>But it is not taking numbers with a decimal point like <code>4.67</code>.
  And it's throwing me an error.
  What type of validation will work on integers and floating point values?
  for example: <code>2</code>, <code>57</code>, <code>54.56</code> should pass but <code>-2.56</code>, <code>-87</code> should fail.</p>