for example, the regex [a-zA-Z] only cares about two kinds of characters: letters and everything else. so instead of individually taking derivatives for 52 alphabet characters a..z, A..Z, we can conclude from the start that there are only two kinds of characters we care about: letters ([a-zA-Z]) and non-letters ([^a-zA-Z]).
В России спрогнозировали стабильное изменение цен на топливо14:55。关于这个话题，PDF资料提供了深入分析
，这一点在PDF资料中也有详细论述
What exactly is climate finance? Who pays it? And who gets it? | Explainer
重点领域突破，发展动能全面提升，更多细节参见爱思助手