Underscores again

[Ed Sawicki]

I've been reading the numerous past threads regarding underscore
characters in DNS names. It seems that most folks here agree that
underscores are not allowed. However, RFC2181 seems to say
something different. Here's the paragraph that confuses me.

"The DNS itself places only one restriction on the particular labels
that can be used to identify resource records.  That one restriction
relates to the length of the label and the full name.  The length of
any one label is limited to between 1 and 63 octets.  A full domain
name is limited to 255 octets (including the separators).  The zero
length full name is defined as representing the root of the DNS tree,
and is typically written and displayed as ".".  Those restrictions
aside, any binary string whatever can be used as the label of any
resource record.  Similarly, any binary string can serve as the value
of any record that includes a domain name as some or all of its value
(SOA, NS, MX, PTR, CNAME, and any others that may be added)."

How should I interpret this?

Ed Sawicki