Parsing is the process of transforming a raw text string into structured data that a program can work with. When a browser converts an HTML string into a DOM tree, when JSON.parse() turns a JSON string into an object, or when a CSV file is split into rows and columns, each of these operations is an instance of parsing.

Parsing typically proceeds in two stages. The first stage, lexical analysis, splits the input string into tokens (the smallest meaningful units). For HTML, this means separating tags like <p> and </p> from the text content between them. The second stage, syntactic analysis, verifies that the sequence of tokens conforms to the grammar rules and builds a tree structure (parse tree) representing the document's hierarchy.

Parsing text in languages like Japanese and Chinese presents unique challenges. English uses spaces to delimit words, making word boundaries explicit. Japanese has no spaces between words, so the string "東京都" could be split as "東京" + "都" (Tokyo + metropolis) or "東" + "京都" (east + Kyoto), depending on context. Morphological analyzers such as MeCab and Janome solve this problem by using dictionaries and statistical models to determine the most natural segmentation. Parsing references on Amazon cover these techniques in depth.

Parse errors can arise from character-related issues. A JSON string literal containing an unescaped newline triggers a parse error. In CSV, a value containing a comma must be enclosed in double quotes; otherwise the parser misidentifies the field boundary. In HTML, failing to escape < or & causes the parser to misinterpret the content as a tag.

From a performance standpoint, parsing is computationally expensive. Calling JSON.parse() on a large JSON file (tens of megabytes) blocks the main thread and freezes the UI. Streaming parsers read data incrementally, parsing it piece by piece, which reduces both latency and memory consumption.

Parsing is also central to how character counting tools work internally. Stripping HTML tags from input text, identifying Markdown syntax elements, and detecting URLs or email addresses are all applications of parsing. Accurate character counting is only possible when the text's structure has been correctly parsed.