是的，它在支持它的浏览器中非常有用，但“限制”是为了方便用户(这样他们就不会被无关的文件淹没)，而不是为了阻止他们上传你不想让他们上传的东西。

它在

找到了 狩猎6 + 火狐9 + 书名: 歌剧11:

下面是你可以使用它的内容类型列表，后面跟着相应的文件扩展名(当然你可以使用任何文件扩展名):

application/envoy   evy
application/fractals    fif
application/futuresplash    spl
application/hta hta
application/internet-property-stream    acx
application/mac-binhex40    hqx
application/msword  doc
application/msword  dot
application/octet-stream    *
application/octet-stream    bin
application/octet-stream    class
application/octet-stream    dms
application/octet-stream    exe
application/octet-stream    lha
application/octet-stream    lzh
application/oda oda
application/olescript   axs
application/pdf pdf
application/pics-rules  prf
application/pkcs10  p10
application/pkix-crl    crl
application/postscript  ai
application/postscript  eps
application/postscript  ps
application/rtf rtf
application/set-payment-initiation  setpay
application/set-registration-initiation setreg
application/vnd.ms-excel    xla
application/vnd.ms-excel    xlc
application/vnd.ms-excel    xlm
application/vnd.ms-excel    xls
application/vnd.ms-excel    xlt
application/vnd.ms-excel    xlw
application/vnd.ms-outlook  msg
application/vnd.ms-pkicertstore sst
application/vnd.ms-pkiseccat    cat
application/vnd.ms-pkistl   stl
application/vnd.ms-powerpoint   pot
application/vnd.ms-powerpoint   pps
application/vnd.ms-powerpoint   ppt
application/vnd.ms-project  mpp
application/vnd.ms-works    wcm
application/vnd.ms-works    wdb
application/vnd.ms-works    wks
application/vnd.ms-works    wps
application/winhlp  hlp
application/x-bcpio bcpio
application/x-cdf   cdf
application/x-compress  z
application/x-compressed    tgz
application/x-cpio  cpio
application/x-csh   csh
application/x-director  dcr
application/x-director  dir
application/x-director  dxr
application/x-dvi   dvi
application/x-gtar  gtar
application/x-gzip  gz
application/x-hdf   hdf
application/x-internet-signup   ins
application/x-internet-signup   isp
application/x-iphone    iii
application/x-javascript    js
application/x-latex latex
application/x-msaccess  mdb
application/x-mscardfile    crd
application/x-msclip    clp
application/x-msdownload    dll
application/x-msmediaview   m13
application/x-msmediaview   m14
application/x-msmediaview   mvb
application/x-msmetafile    wmf
application/x-msmoney   mny
application/x-mspublisher   pub
application/x-msschedule    scd
application/x-msterminal    trm
application/x-mswrite   wri
application/x-netcdf    cdf
application/x-netcdf    nc
application/x-perfmon   pma
application/x-perfmon   pmc
application/x-perfmon   pml
application/x-perfmon   pmr
application/x-perfmon   pmw
application/x-pkcs12    p12
application/x-pkcs12    pfx
application/x-pkcs7-certificates    p7b
application/x-pkcs7-certificates    spc
application/x-pkcs7-certreqresp p7r
application/x-pkcs7-mime    p7c
application/x-pkcs7-mime    p7m
application/x-pkcs7-signature   p7s
application/x-sh    sh
application/x-shar  shar
application/x-shockwave-flash   swf
application/x-stuffit   sit
application/x-sv4cpio   sv4cpio
application/x-sv4crc    sv4crc
application/x-tar   tar
application/x-tcl   tcl
application/x-tex   tex
application/x-texinfo   texi
application/x-texinfo   texinfo
application/x-troff roff
application/x-troff t
application/x-troff tr
application/x-troff-man man
application/x-troff-me  me
application/x-troff-ms  ms
application/x-ustar ustar
application/x-wais-source   src
application/x-x509-ca-cert  cer
application/x-x509-ca-cert  crt
application/x-x509-ca-cert  der
application/ynd.ms-pkipko   pko
application/zip zip
audio/basic au
audio/basic snd
audio/mid   mid
audio/mid   rmi
audio/mpeg  mp3
audio/x-aiff    aif
audio/x-aiff    aifc
audio/x-aiff    aiff
audio/x-mpegurl m3u
audio/x-pn-realaudio    ra
audio/x-pn-realaudio    ram
audio/x-wav wav
image/bmp   bmp
image/cis-cod   cod
image/gif   gif
image/ief   ief
image/jpeg  jpe
image/jpeg  jpeg
image/jpeg  jpg
image/pipeg jfif
image/svg+xml   svg
image/tiff  tif
image/tiff  tiff
image/x-cmu-raster  ras
image/x-cmx cmx
image/x-icon    ico
image/x-portable-anymap pnm
image/x-portable-bitmap pbm
image/x-portable-graymap    pgm
image/x-portable-pixmap ppm
image/x-rgb rgb
image/x-xbitmap xbm
image/x-xpixmap xpm
image/x-xwindowdump xwd
message/rfc822  mht
message/rfc822  mhtml
message/rfc822  nws
text/css    css
text/h323   323
text/html   htm
text/html   html
text/html   stm
text/iuls   uls
text/plain  bas
text/plain  c
text/plain  h
text/plain  txt
text/richtext   rtx
text/scriptlet  sct
text/tab-separated-values   tsv
text/webviewhtml    htt
text/x-component    htc
text/x-setext   etx
text/x-vcard    vcf
video/mpeg  mp2
video/mpeg  mpa
video/mpeg  mpe
video/mpeg  mpeg
video/mpeg  mpg
video/mpeg  mpv2
video/quicktime mov
video/quicktime qt
video/x-la-asf  lsf
video/x-la-asf  lsx
video/x-ms-asf  asf
video/x-ms-asf  asr
video/x-ms-asf  asx
video/x-msvideo avi
video/x-sgi-movie   movie
x-world/x-vrml  flr
x-world/x-vrml  vrml
x-world/x-vrml  wrl
x-world/x-vrml  wrz
x-world/x-vrml  xaf
x-world/x-vrml  xof

Accept属性是在RFC 1867中引入的，目的是为文件选择控件启用基于MIME类型的文件类型过滤。但是到2008年为止，大多数(如果不是全部的话)浏览器都没有使用这个属性。使用客户端脚本，您可以为提交正确类型(扩展)的数据创建一种基于扩展的验证。

其他高级文件上传解决方案需要Flash电影(如SWFUpload)或Java applet(如JUpload)。

If the browser uses this attribute, it is only as an help for the user, so he won't upload a multi-megabyte file just to see it rejected by the server... Same for the <input type="hidden" name="MAX_FILE_SIZE" value="100000"> tag: if the browser uses it, it won't send the file but an error resulting in UPLOAD_ERR_FORM_SIZE (2) error in PHP (not sure how it is handled in other languages). Note these are helps for the user. Of course, the server must always check the type and size of the file on its end: it is easy to tamper with these values on the client side.

Chrome浏览器支持。它不应该用于验证，而是用于类型提示操作系统。如果在文件上传中有accept="image/jpeg"属性，操作系统只能显示建议类型的文件。

It's been a few years, and Chrome at least makes use of this attribute. This attribute is very useful from a usability standpoint as it will filter out the unnecessary files for the user, making their experience smoother. However, the user can still select "all files" from the type (or otherwise bypass the filter), thus you should always validate the file where it is actually used; If you're using it on the server, validate it there before using it. The user can always bypass any client-side scripting.

accept属性非常有用。它提示浏览器只显示当前输入允许的文件。虽然它通常可以被用户覆盖，但默认情况下，它有助于为用户缩小搜索结果的范围，因此他们可以准确地得到他们要找的东西，而不必筛选100种不同的文件类型。

使用

注意:这些示例是基于当前规范编写的，实际上可能无法在所有(或任何)浏览器中运行。规范在将来也可能发生变化，这可能会破坏这些示例。

h1 { font-size: 1em; margin:1em 0; } h1 ~ h1 { border-top: 1px solid #ccc; padding-top: 1em; } <h1>Match all image files (image/*)</h1> <p><label>image/* <input type="file" accept="image/*"></label></p> <h1>Match all video files (video/*)</h1> <p><label>video/* <input type="file" accept="video/*"></label></p> <h1>Match all audio files (audio/*)</h1> <p><label>audio/* <input type="file" accept="audio/*"></label></p> <h1>Match all image files (image/*) and files with the extension ".someext"</h1> <p><label>.someext,image/* <input type="file" accept=".someext,image/*"></label></p> <h1>Match all image files (image/*) and video files (video/*)</h1> <p><label>image/*,video/* <input type="file" accept="image/*,video/*"></label></p>

来自HTML规范(来源)

The accept attribute may be specified to provide user agents with a hint of what file types will be accepted. If specified, the attribute must consist of a set of comma-separated tokens, each of which must be an ASCII case-insensitive match for one of the following: The string audio/* Indicates that sound files are accepted. The string video/* Indicates that video files are accepted. The string image/* Indicates that image files are accepted. A valid MIME type with no parameters Indicates that files of the specified type are accepted. A string whose first character is a U+002E FULL STOP character (.) Indicates that files with the specified file extension are accepted.