"lookbehind" meaning in English

{
  "etymology_text": "Deverbal from look behind.",
  "forms": [
    {
      "form": "lookbehinds",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "lookbehind (countable and uncountable, plural lookbehinds)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English deverbals",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English links with manual fragments",
          "parents": [
            "Links with manual fragments",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Regular expressions",
          "orig": "en:Regular expressions",
          "parents": [
            "Computing",
            "Programming",
            "Technology",
            "Software engineering",
            "All topics",
            "Computer science",
            "Engineering",
            "Software",
            "Fundamental",
            "Sciences",
            "Applied sciences",
            "Media",
            "Communication"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "2004, Mehran Habibi, Java Regular Expressions: Taming the java.util.regex Engine:",
          "text": "[There] are times when it's useful to be able to look to the left of the current position being considered to see what the past had to say about a particular pattern. That is the purpose of lookbehinds.",
          "type": "quote"
        }
      ],
      "glosses": [
        "The analysis of the preceding characters before the regular expression is matched."
      ],
      "hypernyms": [
        {
          "word": "lookaround"
        }
      ],
      "hyponyms": [
        {
          "alt": "?<!",
          "sense": "regular expressions",
          "word": "negative lookbehind"
        },
        {
          "alt": "?<=",
          "sense": "regular expressions",
          "word": "positive lookbehind"
        }
      ],
      "id": "en-lookbehind-en-noun-6XkWsqeC",
      "links": [
        [
          "regular expression",
          "regular expression"
        ],
        [
          "analysis",
          "analysis"
        ],
        [
          "character",
          "character"
        ]
      ],
      "qualifier": "regular expressions",
      "raw_glosses": [
        "(regular expressions) The analysis of the preceding characters before the regular expression is matched."
      ],
      "related": [
        {
          "word": "lookahead"
        },
        {
          "word": "lookaside"
        }
      ],
      "tags": [
        "countable",
        "uncountable"
      ]
    }
  ],
  "word": "lookbehind"
}

{
  "etymology_text": "Deverbal from look behind.",
  "forms": [
    {
      "form": "lookbehinds",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {
        "1": "~"
      },
      "expansion": "lookbehind (countable and uncountable, plural lookbehinds)",
      "name": "en-noun"
    }
  ],
  "hypernyms": [
    {
      "word": "lookaround"
    }
  ],
  "hyponyms": [
    {
      "alt": "?<!",
      "sense": "regular expressions",
      "word": "negative lookbehind"
    },
    {
      "alt": "?<=",
      "sense": "regular expressions",
      "word": "positive lookbehind"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "lookahead"
    },
    {
      "word": "lookaside"
    }
  ],
  "senses": [
    {
      "categories": [
        "English 3-syllable words",
        "English countable nouns",
        "English deverbals",
        "English entries with incorrect language header",
        "English lemmas",
        "English links with manual fragments",
        "English nouns",
        "English terms with quotations",
        "English uncountable nouns",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Regular expressions"
      ],
      "examples": [
        {
          "ref": "2004, Mehran Habibi, Java Regular Expressions: Taming the java.util.regex Engine:",
          "text": "[There] are times when it's useful to be able to look to the left of the current position being considered to see what the past had to say about a particular pattern. That is the purpose of lookbehinds.",
          "type": "quote"
        }
      ],
      "glosses": [
        "The analysis of the preceding characters before the regular expression is matched."
      ],
      "links": [
        [
          "regular expression",
          "regular expression"
        ],
        [
          "analysis",
          "analysis"
        ],
        [
          "character",
          "character"
        ]
      ],
      "qualifier": "regular expressions",
      "raw_glosses": [
        "(regular expressions) The analysis of the preceding characters before the regular expression is matched."
      ],
      "tags": [
        "countable",
        "uncountable"
      ]
    }
  ],
  "word": "lookbehind"
}