[2656] Add API doc for DNAME constructors

src/lib/dns/rdata/generic/dname_39.cc

@@ -31,6 +31,20 @@ using isc::dns::rdata::generic::detail::createNameFromLexer;
 // BEGIN_ISC_NAMESPACE
 // BEGIN_RDATA_NAMESPACE
 
+/// \brief Constructor from string.
+///
+/// The given string must represent a valid DNAME RDATA.  There can be extra
+/// space characters at the beginning or end of the text (which are simply
+/// ignored), but other extra text, including a new line, will make the
+/// construction fail with an exception.
+///
+/// The TARGET must be absolute since there's no parameter that specifies
+/// the origin name; if it is not absolute, \c MissingNameOrigin
+/// exception will be thrown.  These must not be represented as a quoted
+/// string.
+///
+/// \throw Others Exception from the Name and RRTTL constructors.
+/// \throw InvalidRdataText Other general syntax errors.
 DNAME::DNAME(const std::string& namestr) :
     // Fill in dummy name and replace it soon below.
     dname_(Name::ROOT_NAME())
@@ -59,6 +73,22 @@ DNAME::DNAME(InputBuffer& buffer, size_t) :
     // check consistency.
 }
 
+/// \brief Constructor with a context of MasterLexer.
+///
+/// The \c lexer should point to the beginning of valid textual
+/// representation of a DNAME RDATA.  The TARGET field can be
+/// non-absolute if \c origin is non-NULL, in which case \c origin is
+/// used to make it absolute.  It must not be represented as a quoted
+/// string.
+///
+/// \throw MasterLexer::LexerError General parsing error such as missing field.
+/// \throw Other Exceptions from the Name and RRTTL constructors if
+/// construction of textual fields as these objects fail.
+///
+/// \param lexer A \c MasterLexer object parsing a master file for the
+/// RDATA to be created
+/// \param origin If non NULL, specifies the origin of TARGET when it
+/// is non-absolute.
 DNAME::DNAME(MasterLexer& lexer, const Name* origin,
              MasterLoader::Options, MasterLoaderCallbacks&) :
     dname_(createNameFromLexer(lexer, origin))