Select input that is generated and populated with options
A few minors:

Your spacing is a bit inconsistent (e.g. missing spaces here completeSelect{ and here $this-&gt;setIn=$val;)

Your naming convention is a bit inconsistent as well. I don't do much PHP but class names are usually PascalCase. You should decide whether your methods should be camelCase or PascalCase (you have buildOptions vs BuildSelect).

You have a typo here select_brwoser - should probably be select_browser

Your interface into the class is not quite clear. You build your options on construction yet the method to do so is public. Am I supposed to call it again - if so under which circumstances? If the class is immutable (e.g. you can't add more values for the options) then why not simply build the entire select in the first place and cache it?
A possible change would be to make the buildXYZ methods private and build on construction (assuming the class is immutable) and have public getXYZ methods instead which return the cached value for the options or the select respectively.