Flashmode enables simultaneous typesetting as Textures did. When Flashmode, or more precisely one of its applets, is started, it looks for the front most document in TeXShop, gets its path and after that it is hooked forever to this document as long as it stays open, i.e., a few split seconds after Flashmode has started the front most document in the TeXShop could be anything without doing any harm.
Then Flashmode checks in regular Intervals (default is 0.000001 sec), the length of which is user definable—0.000001 sec are recommended for the 8-core Mac Pros—, if its tex document has been modified, and if so, it initiates a save, a pdflatex run, and asks TeXShop to refresh the corresponding pdf file. Flashmode can be invoked even if a document isn’t typeset yet, but beware that its first action will be a typesetting command.
An important feature is that tex syntax errors don’t cause any error messages or disruptions of any kind, i.e., the pdf gets never corrupted, at least the pdf viewer is never aware of it, and the last refreshment is always visible; the pdf viewer will never complain.
Thus, the user never gets any error messages; the presence of errors can only be deduced from the pdf window which then doesn’t change any more; of course the errors will be reported in the log file and can be looked up.
When the tex document is unmodified, Flashmode stays put in the background with very little CPU load: on my machine the idle Flashmode has less than 1%, i.e., Flashmode can stay open as long as one wishes without any bad side effects.
While Flashmode is active, the source document can be typeset independently by TeXShop or by other Scripts or commands, especially other tex tools like bibtex can be run without any interference by Flashmode.
