parse Subroutine

  elemental subroutine parse(self, source, tstart, tend)
  !< Parse the tag contained into a source string.
  !<
  !< It is assumed that the first tag contained into the source string is parsed, the others eventually present are omitted.
  !< Valid syntax are:
  !< + `<tag_name att1="att1 val" att2="att2 val"...>...</tag_name>`
  !< + `<tag_name att1="att1 val" att2="att2 val".../>`
  !< @note Inside the attributes value the symbols `<` and `>` are not allowed.
  class(xml_tag),         intent(inout) :: self      !< XML tag.
  character(*),           intent(in)    :: source    !< String containing the input.
  integer(I4P), optional, intent(out)   :: tstart    !< Starting index of tag inside the string.
  integer(I4P), optional, intent(out)   :: tend      !< Ending index of tag inside the string.
  integer(I4P)                          :: tstartd   !< Starting index of tag inside the string.
  integer(I4P)                          :: tendd     !< Ending index of tag inside the string.

  tstartd = 0
  tendd   = 0
  call self%parse_tag_name(source=source, tstart=tstartd, tend=tendd)
  if (self%tag_name%is_allocated()) then
    if (index(string=source(tstartd:tendd), substring='=')>0) call self%parse_attributes_names(source=source(tstartd:tendd))
    if (index(string=source, substring='</'//self%tag_name//'>')>0) &
      tendd = index(string=source, substring='</'//self%tag_name//'>') + len('</'//self%tag_name//'>') - 1
    call self%get(source=source(tstartd:tendd))
  endif
  if (present(tstart)) tstart = tstartd
  if (present(tend  )) tend   = tendd
  endsubroutine parse