Original text:
2. A naming system associates names with data.  Naming systems have <del> many significant facets that help differentiate them.  Some commonly-identified facets include: </del>  Composition of names the subdomain's name ends with the containing domain's name." (Quoted from RFC1034, Section 3.1).  For example, in the host name "nnn.mmm.example.com", both "mmm.example.com" and <del> "nnn.mmm.example.com" are subdomains of "example.com". </del>  The owner of a CNAME resource record, or a subdomain of the owner of a DNAME resource record (DNAME records are defined in RFC6672). name server side (which is what answers the query) and a resolver side (which performs the resolution function).  Systems operating in this mode are commonly called "recursive servers".  Sometimes <del> they are called "recursive resolvers".  While strictly the difference between these is that one of them sends queries to another recursive server and the other does not, in practice it is not possible to know in advance whether the server that one is </del>  querying will also perform recursion; both terms can be observed in use interchangeably. and controls at a high level."  (Quoted from RFC6841, Section 2) A specialized piece of hardware that is used to create keys for <del> signatures and to sign messages.  In DNSSEC, HSMs are often used to hold the private keys for KSKs and ZSKs and to create the signatures used in RRSIG records at periodic intervals. </del>  Authoritative DNS servers that support DNSSEC often contain software that facilitates the creation and maintenance of DNSSEC

Reviewer comments:
"each other" is clearer in English. I agree that "whole labels" is better and have changed the text.
At line 139, "each other" may be "others" ? At line 358, "full labels" may be "whole labels" or "each label".

Revised text:
2. A naming system associates names with data.  Naming systems have  <ins> many significant facets that help differentiate them from each other.  Some commonly-identified facets include: </ins> Composition of names the subdomain's name ends with the containing domain's name." (Quoted from RFC1034, Section 3.1).  For example, in the host name "nnn.mmm.example.com", both "mmm.example.com" and  <ins> "nnn.mmm.example.com" are subdomains of "example.com".  Note that the comparisons here are done on whole labels; that is, "ooo.example.com" is not a subdomain of "oo.example.com". </ins> The owner of a CNAME resource record, or a subdomain of the owner of a DNAME resource record (DNAME records are defined in RFC6672). name server side (which is what answers the query) and a resolver side (which performs the resolution function).  Systems operating in this mode are commonly called "recursive servers".  Sometimes  <ins> they are called "recursive resolvers".  In practice it is not possible to know in advance whether the server that one is </ins> querying will also perform recursion; both terms can be observed in use interchangeably. and controls at a high level."  (Quoted from RFC6841, Section 2) A specialized piece of hardware that is used to create keys for  <ins> signatures and to sign messages without ever disclosing the private key.  In DNSSEC, HSMs are often used to hold the private keys for KSKs and ZSKs and to create the signatures used in RRSIG records at periodic intervals. </ins> Authoritative DNS servers that support DNSSEC often contain software that facilitates the creation and maintenance of DNSSEC