The regular expression limits the input content in the text box.

<! -- Use regular expressions to restrict Chinese characters only -->
< Input Type = "Text" Onkeyup = "Value = value. Replace (/[^ \ u4e00-\ u9fa5]/g ,'')" Onbeforepaste = "ClipboardData. setdata ('text', clipboardData. getdata ('text'). Replace (/[^ \ u4e00-\ u9fa5]/g ,''))" />


<! -- Use a regular expression to limit that only numbers can be entered -->
< Input Type = "Text" Onkeyup = "Value = value. Replace (/[^ \ D]/g ,'')" Onbeforepaste = "ClipboardData. setdata ('text', clipboardData. getdata ('text'). Replace (/[^ \ D]/g ,''))" />

<! --Only positive integers can be entered using regular expressions-->
<Input type = "text" onkeyup = "value = value. replace (/[^ \ D]/g ,''). replace (/^ 0 \ D {0, 4} $/g, '')" onbeforepaste = "clipboardData. setdata ('text', clipboardData. getdata ('text '). replace (/[^ \ D]/g, '')"/>

<! -- You can only enter numbers and English letters in regular expressions. -->
< Input Type = "Text" Onkeyup = "Value = value. Replace (/[\ W]/g ,'')" Onbeforepaste = "ClipboardData. setdata ('text', clipboardData. getdata ('text'). Replace (/[^ \ D]/g ,''))" />