With AkashaCMS plugins it is easy to generate web pages for a website. While EPUB3 uses HTML5, there are many things one can do with HTML5 which are not allowed in EPUB3. Therefore, when using AkashaCMS tools to write content for an EPUB we need a strategy to convert non-allowed HTML5 constructs into something that's EPUB-safe and makes sense.

That's the role for the akasharender-epub plugin. In this chapter we'll look at what it does.

The source code repository is at (github.com) https://github.com/akashacms/akasharender-epub

As we said earlier, this plugin is invoked with this statement in the Configuration file.

config
    .use(require('akasharender-epub'))

The package.json requires a corresponding dependency to akashacms/akasharender-epub to make the plugin available. As of this writing, the plugin is not published into the npm registry, but is easy enough to use this way.

Forcing XML mode to generate XHTML

EPUB3 requires an XHTML version of HTML5. By default AkashaRender produces HTML files, not XML/XHTML. However that's just a simple configuration away.

The akasharender-epub plugin automatically sets XML mode so that it automatically produces XHTML files.

However, even though the files are in XHTML format, the file extension is .html. That's because AkashaRender's Renderer objects all produce .html filenames.

If the files are not renamed from .html to .xhtml epubcheck will give warnings and it will look like a problem. It's actually not much of a problem, but it's always nicer to have zero warnings and zero errors from a tool like epubcheck.

The epubtools command includes a command epubtools xhtml that converts the .html files to .xhtml files. See Building an EPUB with AkashaEPUB

Removal of <html>/<body> tags from embedded content

Some content retrieved by akashacms-embeddables inserts an <html> tag containing a <body>. This is questionable enough for a website, but in an EPUB it's right out. The <html>/<body> wrapper is removed leaving behind what had been within that wrapper.

Using akashacms-embeddables with an EPUB

The akashacms-embeddables plugin makes it easy to embed content from 3rd party websites. The primary use is when you have a YouTube link, to automatically get the embed code for that video.

For example, take this early video of Ryan Dahl talking about Node.js at Yahoo: (www.youtube.com) https://www.youtube.com/watch?v=M-sc73Y-zQA It can be easily embedded into an AkashaCMS website with:

<embed-resource
        href="https://www.youtube.com/watch?v=M-sc73Y-zQA"
        template="embed-resource-framed.html.ejs"/>

On an AkashaCMS website this shows the title, description, and other information including the embedded viewer. While that's wonderful for a website it's not usable in an EPUB3 eBook. Typical embedded viewers use an <iframe> tag that's simply not allowed in an EPUB.

Here is a live version of that tag:

Ryan Dahl: Introduction to Node.js - YouTube

Source: (www.youtube.com) YUI Library

Ryan Dahl, the creator of Node.js, introduces the project and talks about performance improvements and new architecture. This talk took place at the May 2010...

The problem is, how do you use this construct so it works well in both an EPUB and on a website? To see how to embed EPUB content into a website see Detailed walk-through an embedding EPUB content in an AkashaCMS website

The akashacms-epub plugin doesn't do much to help in this case. Instead, what we do is use an embed-resource-framed.html.ejs partial that does the right thing in an EPUB -- namely to just show the preview image.

The general idea is to fix things so the thumbnail is used instead of the embedded content. The trick is to override certain of the templates provided by akashacms-embeddables, such as embed-resource-framed.html.ejs and embed-resource.html.ejs. In both <%- embedCode %> is used to embed the HTML snippet from the 3rd party website. For example:

<div <%
    if (typeof embedClass !== 'undefined') {
        %>class="<%= embedClass %>" <%
    }
    if (typeof width !== 'undefined' && width) {
        %>width="<%= width %>" <%
    }

    if (typeof style !== 'undefined' && style) {
        %>style="<%= style %>" <%
    }
    %> >
    <h3><%= title %></h3>
    <p>Source: <a href="<%= embedUrl %>" rel="nofollow"><%= embedSource %></a></p>
    <% if ((typeof hideDescription === "undefined" || ! hideDescription) && description) {
    		%><%= description %><%
    	} %>
    <div class="embed-responsive embed-responsive-16by9" <%
    %> style="clear: both;">
        <a href="<%= embedHref %>"><img src="<%= imageUrl %>"/></a>
    </div>
</div>

The key thing is to replace <%- embedCode %> in the standard template with <a href="<%= embedHref %>"><img src="<%= imageUrl %>"/></a>. The imageUrl is the preview image provided by the source website.

See (github.com) https://github.com/akashacms/epub-guide/partials for how that is done in this book.

<a name=""> removal

EPUB doesn't allow the name= attribute on <a> tags, and these are removed.

<h1> etc within a <p>

Sometimes the Markdown processor emits a <h#> tag within a <p> tag. Browsers don't care about this, but epubcheck does. The <p> is removed.

href attributes in <a> and <link> are relativized

Within <a> and <link> tags, if the href attribute points at a local resource, the link must be relative. It's most convenient for the content author to just use /path/to/file.html instead of figuring out the relative path. Such href's are automatically rewritten.

And... for <img> tags, remote images are auto-downloaded

For <img> tags the src= attribute recieves the same treatment for local references. For remote image references, the image is auto-downloaded into a local directory and is automatically bundled into the EPUB.

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