code: func (m *Mux) UseFuncMap(funcMap map[string]interface{}) *Mux {
  	if len(funcMap) == 0 {
  		return m
  	}
  
  	for k, v := range m.SharedFuncs {
  		m.SharedFuncs[k] = v
  	}
  
  	// if template engine is already added (but not loaded)
  	// then it's valid to add these funcs there.
  	for i, n := 0, len(m.Entries); i < n; i++ {
  		// add the shared  funcs if template engine supports funcs.
  		m.SetFuncMapToEngine(funcMap, m.Entries[i].Engine)
  	}
  
  	return m
  }
docs: // UseFuncMap adds shared template funcs to the Mux
  // these funcs are applied to all template engines
  //
  // Should be called not called after Load.