title: How to validate input txt in app inventor 2?
body: <p>My question is related to this <a href="https://stackoverflow.com/questions/29334456/how-to-build-a-tinydb-with-values-from-checkbox-and-textbox-in-app-inventor2">post</a>. I can't figure out, how to validate the text user inputs in the Id1 and Id2 TextBoxes. 
  What I want to achieve is, the Id1 (Textbox) should only accept as input 8 characters in upper case (including spaces), and in the Id2 (Textbox), should be entered only upper case characters (furthermore, it would be great when the user enters something that does not matches these criteria, a notify alert should pop up).</p>
  
  <p>I have tried using the math (> or &lt;) and the text length blocks, without any success but getting a runtime error. Can anyone be kind enough to point me to the right direction regarding this functionality in my app?</p>
  
  <p>Thank you all in advance for your answers.</p>