Selenium.prototype.getTextBoxMaxSize = function(locator)
[
var element = this.browserbot.findElement(locator);
return element.maxLength;
]

How to call :

assertTextBoxMaxSize "TextBox Id" 5

This verify if given textbox has max size is 5, return true if it is, fails otherwise.

Incorporate above code into - user-extensions.js file in selenium-core package