Reindent html with xmllint

Question

I'm trying to reindent current HTML file with this command from inside vim :

:!xmllint --html --format % 2>/dev/null

But, all it does it displays the output to stdout without actually modifying the file.

EDIT0 : I just found this but I'm not sure if this the correct way to do this :

:%!xmllint --html --format - 2>/dev/null

:% stands for the vim range :1,$ (the entire file) and - tells xmllint to read data from stdin

EDIT1 : @statox, Finally, I'll be using equalprg :

autocmd FileType html let &l:equalprg='xmllint --html --format --recover - 2>/dev/null' "Pretty print HTML when 'gg=G' is pressed

Here's some vim help about the let & syntax:

:h let-&
:let &{option-name} = {expr1}                   :let-option :let-&
                        Set option {option-name} to the result of the
                        expression {expr1}.  A String or Number value is
                        always converted to the type of the option.
                        For an option local to a window or buffer the effect
                        is just like using the :set command: both the local
                        value and the global value are changed.
                        Example:
                                :let &path = &path . ',/usr/local/include'
                        This also works for terminal codes in the form t_xx.
                        But only for alphanumerical names.  Example:
                                :let &t_k1 = "\<Esc>[234;"
                        When the code does not exist yet it will be created as
                        a terminal key code, there is no error.

...
:let &l:{option-name} = {expr1}
:let &l:{option-name} .= {expr1}
:let &l:{option-name} += {expr1}
:let &l:{option-name} -= {expr1}
                        Like above, but only set the local value of an option
                        (if there is one).  Works like :setlocal.

:let &g:{option-name} = {expr1}
:let &g:{option-name} .= {expr1}
:let &g:{option-name} += {expr1}
:let &g:{option-name} -= {expr1}
                        Like above, but only set the global value of an option
                        (if there is one).  Works like :setglobal.