A - Anchor
Contents Inline elements except A
Contained in Block-level elements, inline elements except A and BUTTON
The A element denotes an anchor--a hypertext link or the destination of a link. The HREF attribute specifies a hypertext link to another resource, such as an HTML document or a JPEG image.
DIV - Generic Block-level Container
Contents Inline elements, block-level elements
Contained in APPLET, BLOCKQUOTE, BODY, BUTTON, CENTER, DD, DEL, DIV, FIELDSET, FORM, IFRAME, INS, LI, MAP, NOFRAMES, NOSCRIPT, OBJECT, TD, TH
The DIV element defines a generic block-level container, allowing authors to provide style or language information to blocks of content. The element may contain any inline or block-level element, including another DIV.
The DIV element is most useful in combination with the CLASS, ID, or LANG attributes. For example, a navigation bar could be contained within a DIV marked as CLASS=navbar, allowing the author to use style sheets to easily change the background of all navigation bars on a site, or to eliminate navigation bars when printing....
So :
block can store inline element or another block. But inline element can store only inline element.
ex:
Right Example:
<div><a href="#">how</a></div>
<a href="#">show <strong>Bold</strong></a>
Wrong Example:
<a href="#"><div>How</div></a>