code: func (t *tScreen) buildAcsMap() {
  	acsstr := t.ti.AltChars
  	t.acs = make(map[rune]string)
  	for len(acsstr) > 2 {
  		srcv := acsstr[0]
  		dstv := string(acsstr[1])
  		if r, ok := vtACSNames[srcv]; ok {
  			t.acs[r] = t.ti.EnterAcs + dstv + t.ti.ExitAcs
  		}
  		acsstr = acsstr[2:]
  	}
  }
docs: // buildAcsMap builds a map of characters that we translate from Unicode to
  // alternate character encodings.  To do this, we use the standard VT100 ACS
  // maps.  This is only done if the terminal lacks support for Unicode; we
  // always prefer to emit Unicode glyphs when we are able.