This option enables you to specify the name of the attribute to check if it's value is true/false. If the mode option is set to "specific_textareas", only specific textareas with a attribute by the name of the value of this option gets converted and only if it's set to true. This option defaults to "mce_editable".
If the mode is set to textareas and the textarea trigger attribute value is set to false, these textareas will not be converted.
Example of usage of the textarea_trigger option:
tinyMCE.init({
...
textarea_trigger : "convert_this"
});