PHPSpellCheck can be set to spell check one or multiple fields by their ID attribute. This is done using the Fields property of either the SpellCheckButton or SpellAsYouType Class.
The ID can refer to any Textarea, Text Input, HTML Element or IFrame.
<textarea id='MyField' ></textarea>
<?php
# PHP Spell Check 1 Field in a Pop-up Dialog
require "/phpspellcheck/include.php";
$mySpell = new SpellCheckButton();
$mySpell->InstallationPath = "/phpspellcheck/";
$mySpell->Fields = "MyField";
echo $mySpell->SpellImageButton();
?>on();
<textarea id='MyField' ></textarea>
<?php
# PHP Spell Check 1 Field in Situ
$mySpell = new SpellAsYouType();
$mySpell->InstallationPath = "/phpspellcheck/";
$mySpell->Fields = "MyField";
echo $mySpell->Activate();
?>
To target multiple fields - use a comma separated list of Ids:
$mySpell->Fields = "MyField1,MyHTMLElement2,MyIFrame3,MyTextInput4";