The "Menu Structure Source" property allows you to specify how your menu is populated with menu items (and submenus):

Option 1
(default option)

Using the project's structure, i.e. items that you add to your AllWebMenus project. These items are fetched from its compiled project's file.

Option 2

"On-the-fly", using <UL><LI> items fetched from the loaded page that shows the menu.
Menu Structure (items/submenus that populate the menu)
Your menu uses the same menu structureon different pages.This structure is edited within AllWebMenus and compiled to a single javascript file used by all your web pages.With this option, you do not have to add any menu items (<UL><LI> HTML code) on each page of your website.

When you want to change your menu, you just edit it, re-compile and re-upload its related files and you are done (for all your web pages).

 Your menu can use a different menu structure on different pages. (optional)How?

Since the menu is built "on-the-fly", based on <UL><LI> tags inside your pages' HTML code, you can use different tags for different pages, thus creating a menu with different items/submenus.

With this option, to update your menu structure requires that you update all web pages containing its <UL><LI> menu structure.
Styles (appearance/behavior)
The menu appearance is based on the styles of Style Editor andany *custom*, item-specific style values you add.Every single item/submenu can be different if you like. The menu appearance is based on the styles of Style Editor only.Any *custom*, item-specific style values are *ignored*.

All items using the same style appear the same (no further customizations).

(note: the project's structure is still used in "Menu Preview Pane" to show you sample items when designing your menu)
Menu execution/rendering
The menu starts executing while the page is still loading, not after. The menu always appears after the page is fully loaded.The menu engine starts building the menu only after the entire page is fully loaded. With this technique, the existence of any nested tags do not break the execution and rendering of the menu.The only minimal "effect" of this option is that your menu appears after the page is fully loaded, not as quickly as in the other option. However, this is very minimal and unnoticeable in most cases, as the menu files are cached after visiting the first page that contains them.
SEO capabilities
Both "sitemap-based SEO" and "on-page SEO" Read more on SEO options Both "sitemap-based SEO" and "on-page SEO"(note: "on-page SEO" is inherent here)

Example of the <UL><LI> menu structure (option 2):

<ul id="awmULLI-menu" style="position:absolute;left:-999px;">
<li><a href="index.html">Home</a></li>

<li><a href="item1.html">Item 1</a></li>

<li><a href="item2.html">Item 2</a>

<ul>

<li>Item 2.1

<ul>

<li><a href="item_211.html">Item 2.1.1</a></li>

<li><a href="item_212.html">Item 2.1.2</a></li>

<li><a href="item_213.html">Item 2.1.3</a></li>

<li><a href="item_214.html">Item 2.1.4</a></li>

</ul>

</li>

<li><a href="item_22.html">Item 2.2</a>

</li>

</ul>

</li>

<li><a href="item3.html">Item 3</a>

</li>

</ul>

When added to a page linked to your menu, the above <UL><LI> HTML code produces the following menu structure "on-the-fly":

<UL> <LI> sample menu structure

Online Example: http://www.likno.com/examples/seo-css-menu.html

You may also read the related HELP topic inside AllWebMenus, which provides more details on this feature.