Spell checking can be switched on and off from the Tools menu or by assigning an accelerator key to this command. The switch only affects the currently active document. Spell checking is performed via an syntax colouring algorithm that provides an alternative to the various algorithms for differing types of source code.
Plato loads valid words from the file English.lex and colours them using the text "Foreground" colour. Invalid words are coloured using the "Error" colour (both colours can be configured in the Fonts and Colours section of the Options dialog). You can provide alternative files to English.lex but you must specify its name in the Options dialog. The file must contain words made up from the 26 standard alphabetic characters in the ranges a - z and A - Z. The apostrophe, hyphen and underscore are also recognised. Words must be separated by spaces or linefeeds. They need not be in dictionary order.
A word that appears as invalid can be added to the dictionary by using the popup menu. These additional words are treated as user keywords and stored in Plato3.ini. You can include these words in your .lex file by issuing a command to Export the dictionary. This command can be found in the Keyboard section of the Options dialog under the name Spelling.Export. The file called English.lex is treated as read-only so you are prompted to export to a file with a different name.
You would normally use spell checking with plain text files but you can also switch it on for source code if it contains text that you would like to check.