解释划线的字：
板印书籍：                         唐人尚未盛为之:                 
五代时始印五经：                   已后：                          
有布衣毕升：                       又为活板：                       
火烧令坚：                         先设一铁板：                    
其上以松脂、蜡和纸灰之类冒之：                                       
乃密布字印：                       持就火炀之：                     
则字平如砥：                       一板已自布字：                   
第二板已具：                       更互用之：                       
瞬息可就：                         每韵为一帖：                        
以纸帖之：                          有奇字素无备者：                 
旋刻之：                           不若燔土：                       
用讫再火令药熔：                    殊不沾污：                       
若止印三二本