Here are some of the features you can get in Xselerator:
Editor
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* Clear and easy to use IDE;
* XSL/XSLT element and attribute intuitive (like Intellisense or code insight) drop-downs;
* Automatic tag completion - in XSL/XSLT tag completion follows model and, optionally, fills element with mandatory attributes;
* HTML element and attribute intuitive drop-downs;
* Unicode Support
* Full XSL, XSLT, XML and HTML color syntax highlighting (fully customizable);
* All the usual editor capabilities (cut, copy, paste, find, replace) plus special 'Copy as RTF' and 'Copy as HTML' features allowing syntax highlighting to be preserved when copying and pasting to word-processors, html editors and newsgroups etc.;

XSLT debugger
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* Full stepping capability;
* Breakpoints on both XSLT and input XML;
* Conditional breakpoints;
* View template call stack;
* Watch values (including full XPath expression watches);
* Optional stepping into built-in rules
* Uses MSXML3 transformations (so that debugging session behavior matches a * real, production environment transformation engine);

Transformation
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* One click transformation test;
* Full transformation testing (including XSL parameter passing, start mode and output test path);
* Use of alternative command line transformation engines (e.g. Instant Saxon, XT, etc.)

Wizards
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* For building tables,
* Selects/list boxes and
* XSLT grouping/distinct expressions;

Tools
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* XPath query analyzer (test XPath queries to see the resulting node sets - click on resulting list item to view position to node in source/tree view);
* Project Files Manager, which keeps all your related XML and XSL files together;
* Source edit, tree and browser view (requires IE5.x) modes;
* Files opened history (re-open previous files from menu - re-opened XSLT files restore previous parameters/start mode);
* Print and print preview (with selectable highlighting options);