Module:If preview/configuration

This Lua module is used in system messages, and on approximately ༣༠༧,༠༠༠ pages, or roughly 6935% of all pages.
Changes to it can cause immediate changes to the Wikipedia user interface.
To avoid major disruption and server load, any changes should be tested in the module's /sandbox or /testcases subpages, or in your own module sandbox. The tested changes can be added to this page in a single edit. Please discuss changes on the talk page before implementing them.

--[[
We perform the actual check for whether this is a preview here since
preprocessing is relatively expensive.
]]
local frame = mw.getCurrentFrame()

local function is_preview()
	local revision_id = frame:preprocess('{{REVISIONID}}')
	-- {{REVISIONID}} is usually the empty string when previewed.
	-- I don't know why we're checking for nil but hey, maybe someday things
	-- would have broken
	return revision_id == nil or revision_id == ''
end

local function templatestyles()
	return frame:extensionTag{
		name = 'templatestyles', args = { src = 'Module:If preview/styles.css' }
	}
end

return {
	preview = is_preview(),
	templatestyles = templatestyles(),
	warning_infrastructure = '%s<div class="preview-warning"><strong>Preview warning:</strong> %s</div>',
	missing_warning = 'The template has no warning text. Please add a warning.'
}