@daniel-sanches-0, could you please include the complete XML output that you are seeing? (You may be able to exclude large, irrelevant portions of the content), but there may be relevant xmlns attributes higher up in the XML tree.

Also, how are you adding the signature to your XML and getting your XML content back out from the objects?

Ken,

Can you be more specific about the non-printing characters? If you are serializing  data to XML, you need to be clear about whether you are correctly XML-escaping the characters, or whether you are actually receiving values that are not permitted in XML. Is it clear as to which of these problems you are running into?

A rather subtle point that I haven't seen discussed here is actually about how TSTART/TCOMMIT/TROLLBACK should be handled when triggering a TROLLBACK from code that may be part of a nested transaction. Given that a lot of the code I write may be called from various contexts and those calling contexts may already have open transactions, my preferred transaction pattern is as follows:

Method SaveSomething() As %Status {
  Set tStatus = $$$OK
  Set tInitTLevel = $TLevel
  Try {
    // Validate input before opening transaction so you can exit before incurring any major overhead
    TSTART
    // Do thing 1
    // Do thing 2
    // Check status or throw exception
    TCOMMIT
  }
  // Handle exception locally due to local cleanup needs
  Catch ex {
    Set tStatus = ex.AsStatus()
  }
  While ($TLevel > tInitTLevel) {
    // Only roll back one transaction level as you make it possible for the caller to decide whether the whole transaction should be rolled back
    TRollback 1
  }
  Quit tStatus
}

(Edited for formatting.)

I prefer doing this more correctly using the right API for matching status values:

If $system.Status.Equals(sc,$$$ERRORCODE($$$GeneralError),$$$ERRORCODE($$$MoreSpecificStatusCode),...) {
  // Handle specific error(s)
}

The use of ' can result in unexpected behaviour when you are checking for a 4 digit code, but are handling a 3 digit code...

Note that it's also safer to wrap status codes in $$$ERRORCODE($$$TheErrorCode), but that may not be necessary depending on the specific context.