What it is
XHTML stands for Extensible HyperText Markup Language. It uses HTML elements with XML syntax rules. Those rules require the document’s structure to be written more strictly.
Why it matters
Understanding XHTML helps me recognize why some web documents require more exact syntax than others. Software that processes XHTML as XML expects a well-formed document and can report an error if the syntax is incorrect.
Rules I practiced
In my CYB 240 lab, I learned that XHTML requires:
- Elements to be properly nested.
- Elements to be closed, including empty elements.
- HTML element names to be lowercase.
- Attribute values to be placed inside quotation marks.
Example
A line break in HTML can be written as:
<br>In XHTML, the empty element is closed:
<br />A properly nested example looks like this:
<p>This is <strong>important</strong> text.</p>The <strong> element closes before the paragraph closes.
Security connection
During the lab, I reviewed a login page and its HTML source from a pentester’s perspective. Looking at page structure can help identify form fields and understand what the browser sends to an application.
Correct markup alone does not secure a login. The application also needs appropriate protections when it handles user input.
Resources
- CYB 240: Application Security - Module One lab, Exploring HTML.