Tell It Like It Is: Text-to-Speech (TTS)

The first step is to include an entry for the PLS file in the EPUB manifest:

<item href="lexicon.pls" id="pls" media-type="application/pls+xml"/>

The href attribute defines the location of the file relative to the package document and the media-type attribute value “application/pls+xml” identifies to a reading system that we’ve attached a PLS file.

Including one or more PLS files does not mean they apply by default to all your content, however; in fact, they apply to none of it by default. You next have to explicitly tie each PLS lexicon to each XHTML content document it is to be used with by adding a link element to the document’s header:

<html …>
    <head>
        …
        <link
            rel="pronunciation"
            href="lexicon.pls"
            type="application/pls+xml"
            hreflang="en" />
        …
    </head>
    …
</html>

There are a number of differences between the declaration for the PLS file in the publication manifest above and in the content file here. The first is the use of the rel attribute to include an explicit relationship (that the referenced file represents pronunciation information). This attribute represents somewhat redundant information, however, since the media type is once again specified (here in the type attribute). But as it is a required attribute in HTML5, it can’t be omitted.

The HTML link element also includes an additional piece of information to allow selective targeting of lexicons: the hreflang attribute. This attribute specifies the language to which the included pronunciations apply. For example, if you have an English document (as defined in the xml:lang attribute on the html root element) that embeds French prose, you could include two lexicon files:

<link
    rel="pronunciation"
    href="lexicon/en.pls"
    type="application/pls+xml"
    hreflang="en" />

<link
    rel="pronunciation"
    href="lexicon/fr.pls"
    type="application/pls+xml"
    hreflang="fr" />

Assuming all your French passages have xml:lang attributes on them, the reading system can selectively apply the lexicons to prevent any possible pronunciation confusion:

<p>It's the Hunchback of <i xml:lang="fr">Notre Dame</i> not of Notre Dame.</p>

A unilingual person reading this prose probably would not understand the distinction being made here: that the French pronunciation is not the same as the Americanization. Including separate lexicons by language, however, would ensure that readers would hear the Indiana university name differently than the French cathedral if they turn on TTS:

<lexicon
    version="1.0"
    alphabet="x-sampa"
    xml:lang="en"
    xmlns="http://www.w3.org/2005/01/pronunciation-lexicon">
    <lexeme>
        <grapheme>Notre Dame</grapheme>
        <phoneme>noUt@r 'deIm</phoneme>
    </lexeme>
</lexicon>

<lexicon
    version="1.0"
    alphabet="x-sampa"
    xml:lang="fr"
    xmlns="http://www.w3.org/2005/01/pronunciation-lexicon">
    <lexeme>
        <grapheme>Notre Dame</grapheme>
        <phoneme>n%oUtr@ d"Am</phoneme>
    </lexeme>
</lexicon>

When the contents of the i tag are encountered, and identified as French, the pronunciation from the corresponding lexicon gets applied instead of the one from the default English lexicon.