I am using inline styles in spans because I am making an email CMS which means certain elements need to be styled inline so they will be universally read across email clients. What I encounter with WordPress is bold injects <strong> italic <em> however underline injects <span style="text-decoration: underline;">
I want to be able to use span and the appropriate inline style property. The version of WordPress I am using is bundled with tinymce, a wysiwyg editor. I read a little bit about overriding the formats for tinymce TinyMCE Formats
It looks like much of the tinyMCE is defined in this PHP include
/wp-includes/class-wp-editor.php
I am still not sure how to go about overriding the definitions. I was thinking there ought to be a way of overriding them in my theme’s functions.php
The WordPress Codex has a whole page on TinyMCE Custom Styles, including code samples that should help get you started. You might also want to look at add_editor_style() to register a custom editor stylesheet to apply some of the styles within the editor window itself.