DOC-BUG: Security considerations for parsing records

I haven't seen this mentioned in the drafts, but I remember someone 
Bellovin bringing this up in a different forum in regards to SPF a few 
months ago. Among the two RR formats for Sender-ID, is the TXT format. 
As Steve pointed out, parsing any kind of free form data can potentially 
lead to security issues if the parsers are not written properly (such as 
buffer overruns). Therefore, it might be useful to add a section or just 
a few sentences to mention that issue.
Yakov