code: func (f *Fpdf) ClipText(x, y float64, txtStr string, outline bool) {
  	f.clipNest++
  	f.outf("q BT %.5f %.5f Td %d Tr (%s) Tj ET", x*f.k, (f.h-y)*f.k, intIf(outline, 5, 7), f.escape(txtStr))
  }
docs: // ClipText begins a clipping operation in which rendering is confined to the
  // character string specified by txtStr. The origin (x, y) is on the left of
  // the first character at the baseline. The current font is used. outline is
  // true to draw a border with the current draw color and line width centered on
  // the perimeters of the text characters. Only the outer half of the border
  // will be shown. After calling this method, all rendering operations (for
  // example, Image(), LinearGradient(), etc) will be clipped. Call ClipEnd() to
  // restore unclipped operations.