规定上传文件的类型
Valid Accept Types: For CSV files (.csv), use: <input type="file" accept=".csv" /> For Excel Files 2003-2007 (.xls), use: <input type="file" accept="application/vnd.ms-excel" /> For Excel Files 2010 (.xlsx), use: <input type="file" accept="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet" /> For Text Files (.txt) use: <input type="file" accept="text/plain" /> For Image Files (.png/.jpg/etc), use: <input type="file" accept="image/*" /> For HTML Files (.htm,.html), use: <input type="file" accept="text/html" /> For Video Files (.avi, .mpg, .mpeg, .mp4), use: <input type="file" accept="video/*" /> For Audio Files (.mp3, .wav, etc), use: <input type="file" accept="audio/*" /> For PDF Files, use: <input type="file" accept=".pdf" />