I like to do my programming, these days, for my TI99 using a PC. First off I can use the wonderful Notepad++ for editing and test the software in the equally wonderful MAME and secondly I don't wear out my 40+ old TI99/4a. And to increase the already massive wonderfulness I have added language support for the TI99 to the already extensive list of programming languages built into Notepad++. 

I added TMS9900 and TI99 XB support to Notepad++ with the two .XML files attached in the .ZIP below. 

To add language support for TMS9900 & TI88 XB to Notepad++ use | Language>User Defined Language>Define Your Language. on the 'Define...' page click the Import button and add one .XML file at a time. Shutdown Notepad++ then restart and TMS9900 & TI XB will now be a choice in the Language list.

Note: the TI XB works well with AdvBASIC of the Geneve too.

I then use Classic99 and paste straight in XB or for Geneve ABASIC I use TIImageTool to import the file into a .dsk or .hd by | Edit>'Import from Text Editor' then paste>save the file. For TMS9900 a cross compiler would work nicely as well as the other two previous methods. 

that's it. Enjoy.

notepad++-xml-lang-files.zip