HTML vs XHTML
Case Sensitivity
In HTML case does not matter for tag names and attribute names
<BODY>, <Body>, and <body> are equivalent. <H1 ALIGN="..."> is equivalent to <H1 aLiGn="...">
In xhtml, tag names and attribute names must be in lower case
<body>, <h1 align="...">
HTML - XHTML - Quotes
In HTML quotes are optional if attribute value contains only alphanumeric values
- <H1 ALIGN="LEFT"> or <H1 ALIGN=LEFT>
In xhtml, you must always use single or double quotes
- <h1 align="left"> or <h1 align='left'>
HTML - XHTML Tags Handling
In HTML some tags are containers
- <H1>...</H1>, <A HREF...>...</A>
In HTML some tags are standalone
- <BR>, <HR>
In HTML Some tags have optional end tags
- <P>, <LI>, <TR>, <TD>, <TH>
In XHTML All tags are containers. End tags always required.
- <p>...</p>, <li>...</li>
In XHTML if there is no body content, start/end tags can be merged
- <br></br> or just <br/>