man: update lvmreport man page about json_std format

man/lvmreport.7_main

@@ -1303,9 +1303,19 @@ binary_values_as_numeric=1
 .
 LVM can output reports in different formats - use \fBreport/output_format\fP
 configuration setting (or \fB--reportformat\fP command line option) to swith
-the report output format. Currently, LVM supports \fB"basic"\fP (all the examples
+the report output format.
-we used above used this format) and \fB"JSON"\fP output format.
+
 .P
+Currently, LVM supports these outpout formats:
+.RS
+- \fB"basic"\fP (all the examples we used above used this format),
+.br
+- \fB"json"\fP,
+.br
+- \fB"json_std"\fP.
+.RE
+.P
+For example:
 .nf
 # lvs -o lv_name,lv_size --reportformat json
   {
@@ -1320,13 +1330,23 @@ we used above used this format) and \fB"JSON"\fP output format.
   }
 .fi
 .P
+The \fBjson_std\fP output format is more compliant with JSON standard and
+compared to the original \fBjson\fP format:
+.RS
+- it does not use double quotes around numeric values,
+.br
+- it uses 'null' for undefined numeric values,
+.br
+- it prints string list as proper JSON array of strings instead of a single string.
+.RE
+.P
 Note that some configuration settings and command line options have no
-effect with certain report formats. For example, with \fBJSON\fP output,
+effect with certain report formats. For example, with \fBjson\fP or
-it doesn't have any meaning to use \fBreport/aligned\fP (\fB--aligned\fP),
+\fBjson_std\fP output, it doesn't have any meaning to use \fBreport/aligned\fP
-\fBreport/noheadings\fP (\fB--noheadings\fP), \fBreport/columns_as_rows\fP
+(\fB--aligned\fP), \fBreport/noheadings\fP (\fB--noheadings\fP),
-(\fB--rows\fP) or \fBreport/buffered\fP (\fB--unbuffered\fP). All these
+\fBreport/columns_as_rows\fP (\fB--rows\fP) or \fBreport/buffered\fP
-configuration settings and command line options are ignored if using the
+(\fB--unbuffered\fP). All these configuration settings and command line options
-\fBJSON\fP report output format.
+are ignored if using the \fBjson\fP or \fBjson_std\fP report output format.
 .
 .SS Selection
 .