Copy the sample XML syntax highlight file to the user's home directory:

% cp /usr/local/share/nano/xml.nanorc ~/.nanorc

Use an editor to replace the lines in the ~/.nanorc syntax "xml" block with these rules:

syntax "xml" "\.([jrs]html?|xml|xslt?)$"
# trailing whitespace
color ,blue "[[:space:]]+$"
# multiples of eight spaces at the start a line
# (after zero or more tabs) should be a tab
color ,blue "^([TAB]*[ ]{8})+"
# tabs after spaces
color ,yellow "( )+TAB"
# highlight indents that have an odd number of spaces
color ,red "^(([ ]{2})+|(TAB+))*[ ]{1}[^ ]{1}"
# lines longer than 70 characters
color ,yellow "^(.{71})|(TAB.{63})|(TAB{2}.{55})|(TAB{3}.{47}).+$"

Process the file to create embedded tabs:

% perl -i'' -pe 's/TAB/\t/g' ~/.nanorc

Specify additional helpful options when running the editor:

% nano -AKipwz -r 70 -T8 chapter.xml

Users of csh(1) can define an alias in ~/.cshrc to automate these options:

alias nano "nano -AKipwz -r 70 -T8"

After the alias is defined, the options will be added automatically:

% nano chapter.xml