kmx.io/prism.js

diff --git a/components/prism-asciidoc.js b/components/prism-asciidoc.js
index 486ca12..8909f14 100644
--- a/components/prism-asciidoc.js
+++ b/components/prism-asciidoc.js
@@ -35,7 +35,7 @@
 			pattern: /^\|={3,}(?:(?:\r?\n|\r(?!\n)).*)*?(?:\r?\n|\r)\|={3,}$/m,
 			inside: {
 				'specifiers': {
-					pattern: /(?!\|)(?:(?:(?:\d+(?:\.\d+)?|\.\d+)[+*])?(?:[<^>](?:\.[<^>])?|\.[<^>])?[a-z]*)(?=\|)/,
+					pattern: /(?:(?:(?:\d+(?:\.\d+)?|\.\d+)[+*](?:[<^>](?:\.[<^>])?|\.[<^>])?|[<^>](?:\.[<^>])?|\.[<^>])[a-z]*|[a-z]+)(?=\|)/,
 					alias: 'attr-value'
 				},
 				'punctuation': {
diff --git a/components/prism-asciidoc.min.js b/components/prism-asciidoc.min.js
index 9df7613..dc59cbf 100644
--- a/components/prism-asciidoc.min.js
+++ b/components/prism-asciidoc.min.js
@@ -1 +1 @@
-!function(t){var n={pattern:/(^[ \t]*)\[(?!\[)(?:(["'$`])(?:(?!\2)[^\\]|\\.)*\2|\[(?:[^\[\]\\]|\\.)*\]|[^\[\]\\"'$`]|\\.)*\]/m,lookbehind:!0,inside:{quoted:{pattern:/([$`])(?:(?!\1)[^\\]|\\.)*\1/,inside:{punctuation:/^[$`]|[$`]$/}},interpreted:{pattern:/'(?:[^'\\]|\\.)*'/,inside:{punctuation:/^'|'$/}},string:/"(?:[^"\\]|\\.)*"/,variable:/\w+(?==)/,punctuation:/^\[|\]$|,/,operator:/=/,"attr-value":/(?!^\s+$).+/}},a=t.languages.asciidoc={"comment-block":{pattern:/^(\/{4,})(?:\r?\n|\r)(?:[\s\S]*(?:\r?\n|\r))??\1/m,alias:"comment"},table:{pattern:/^\|={3,}(?:(?:\r?\n|\r(?!\n)).*)*?(?:\r?\n|\r)\|={3,}$/m,inside:{specifiers:{pattern:/(?!\|)(?:(?:(?:\d+(?:\.\d+)?|\.\d+)[+*])?(?:[<^>](?:\.[<^>])?|\.[<^>])?[a-z]*)(?=\|)/,alias:"attr-value"},punctuation:{pattern:/(^|[^\\])[|!]=*/,lookbehind:!0}}},"passthrough-block":{pattern:/^(\+{4,})(?:\r?\n|\r)(?:[\s\S]*(?:\r?\n|\r))??\1$/m,inside:{punctuation:/^\++|\++$/}},"literal-block":{pattern:/^(-{4,}|\.{4,})(?:\r?\n|\r)(?:[\s\S]*(?:\r?\n|\r))??\1$/m,inside:{punctuation:/^(?:-+|\.+)|(?:-+|\.+)$/}},"other-block":{pattern:/^(--|\*{4,}|_{4,}|={4,})(?:\r?\n|\r)(?:[\s\S]*(?:\r?\n|\r))??\1$/m,inside:{punctuation:/^(?:-+|\*+|_+|=+)|(?:-+|\*+|_+|=+)$/}},"list-punctuation":{pattern:/(^[ \t]*)(?:-|\*{1,5}|\.{1,5}|(?:[a-z]|\d+)\.|[xvi]+\))(?= )/im,lookbehind:!0,alias:"punctuation"},"list-label":{pattern:/(^[ \t]*)[a-z\d].+(?::{2,4}|;;)(?=\s)/im,lookbehind:!0,alias:"symbol"},"indented-block":{pattern:/((\r?\n|\r)\2)([ \t]+)\S.*(?:(?:\r?\n|\r)\3.+)*(?=\2{2}|$)/,lookbehind:!0},comment:/^\/\/.*/m,title:{pattern:/^.+(?:\r?\n|\r)(?:={3,}|-{3,}|~{3,}|\^{3,}|\+{3,})$|^={1,5} .+|^\.(?![\s.]).*/m,alias:"important",inside:{punctuation:/^(?:\.|=+)|(?:=+|-+|~+|\^+|\++)$/}},"attribute-entry":{pattern:/^:[^:\r\n]+:(?: .*?(?: \+(?:\r?\n|\r).*?)*)?$/m,alias:"tag"},attributes:n,hr:{pattern:/^'{3,}$/m,alias:"punctuation"},"page-break":{pattern:/^<{3,}$/m,alias:"punctuation"},admonition:{pattern:/^(?:TIP|NOTE|IMPORTANT|WARNING|CAUTION):/m,alias:"keyword"},callout:[{pattern:/(^[ \t]*)<?\d*>/m,lookbehind:!0,alias:"symbol"},{pattern:/<\d+>/,alias:"symbol"}],macro:{pattern:/\b[a-z\d][a-z\d-]*::?(?:[^\s\[\]]*\[(?:[^\]\\"']|(["'])(?:(?!\1)[^\\]|\\.)*\1|\\.)*\])/,inside:{function:/^[a-z\d-]+(?=:)/,punctuation:/^::?/,attributes:{pattern:/(?:\[(?:[^\]\\"']|(["'])(?:(?!\1)[^\\]|\\.)*\1|\\.)*\])/,inside:n.inside}}},inline:{pattern:/(^|[^\\])(?:(?:\B\[(?:[^\]\\"']|(["'])(?:(?!\2)[^\\]|\\.)*\2|\\.)*\])?(?:\b_(?!\s)(?: _|[^_\\\r\n]|\\.)+(?:(?:\r?\n|\r)(?: _|[^_\\\r\n]|\\.)+)*_\b|\B``(?!\s).+?(?:(?:\r?\n|\r).+?)*''\B|\B`(?!\s)(?:[^`'\s]|\s+\S)+['`]\B|\B(['*+#])(?!\s)(?: \3|(?!\3)[^\\\r\n]|\\.)+(?:(?:\r?\n|\r)(?: \3|(?!\3)[^\\\r\n]|\\.)+)*\3\B)|(?:\[(?:[^\]\\"']|(["'])(?:(?!\4)[^\\]|\\.)*\4|\\.)*\])?(?:(__|\*\*|\+\+\+?|##|\$\$|[~^]).+?(?:(?:\r?\n|\r).+?)*\5|\{[^}\r\n]+\}|\[\[\[?.+?(?:(?:\r?\n|\r).+?)*\]?\]\]|<<.+?(?:(?:\r?\n|\r).+?)*>>|\(\(\(?.+?(?:(?:\r?\n|\r).+?)*\)?\)\)))/m,lookbehind:!0,inside:{attributes:n,url:{pattern:/^(?:\[\[\[?.+?\]?\]\]|<<.+?>>)$/,inside:{punctuation:/^(?:\[\[\[?|<<)|(?:\]\]\]?|>>)$/}},"attribute-ref":{pattern:/^\{.+\}$/,inside:{variable:{pattern:/(^\{)[a-z\d,+_-]+/,lookbehind:!0},operator:/^[=?!#%@$]|!(?=[:}])/,punctuation:/^\{|\}$|::?/}},italic:{pattern:/^(['_])[\s\S]+\1$/,inside:{punctuation:/^(?:''?|__?)|(?:''?|__?)$/}},bold:{pattern:/^\*[\s\S]+\*$/,inside:{punctuation:/^\*\*?|\*\*?$/}},punctuation:/^(?:``?|\+{1,3}|##?|\$\$|[~^]|\(\(\(?)|(?:''?|\+{1,3}|##?|\$\$|[~^`]|\)?\)\))$/}},replacement:{pattern:/\((?:C|TM|R)\)/,alias:"builtin"},entity:/&#?[\da-z]{1,8};/i,"line-continuation":{pattern:/(^| )\+$/m,lookbehind:!0,alias:"punctuation"}};function i(t){for(var n={},i=0,e=(t=t.split(" ")).length;i<e;i++)n[t[i]]=a[t[i]];return n}n.inside.interpreted.inside.rest=i("macro inline replacement entity"),a["passthrough-block"].inside.rest=i("macro"),a["literal-block"].inside.rest=i("callout"),a.table.inside.rest=i("comment-block passthrough-block literal-block other-block list-punctuation indented-block comment title attribute-entry attributes hr page-break admonition list-label callout macro inline replacement entity line-continuation"),a["other-block"].inside.rest=i("table list-punctuation indented-block comment attribute-entry attributes hr page-break admonition list-label macro inline replacement entity line-continuation"),a.title.inside.rest=i("macro inline replacement entity"),t.hooks.add("wrap",function(t){"entity"===t.type&&(t.attributes.title=t.content.replace(/&amp;/,"&"))}),t.languages.adoc=t.languages.asciidoc}(Prism);
\ No newline at end of file
+!function(t){var n={pattern:/(^[ \t]*)\[(?!\[)(?:(["'$`])(?:(?!\2)[^\\]|\\.)*\2|\[(?:[^\[\]\\]|\\.)*\]|[^\[\]\\"'$`]|\\.)*\]/m,lookbehind:!0,inside:{quoted:{pattern:/([$`])(?:(?!\1)[^\\]|\\.)*\1/,inside:{punctuation:/^[$`]|[$`]$/}},interpreted:{pattern:/'(?:[^'\\]|\\.)*'/,inside:{punctuation:/^'|'$/}},string:/"(?:[^"\\]|\\.)*"/,variable:/\w+(?==)/,punctuation:/^\[|\]$|,/,operator:/=/,"attr-value":/(?!^\s+$).+/}},a=t.languages.asciidoc={"comment-block":{pattern:/^(\/{4,})(?:\r?\n|\r)(?:[\s\S]*(?:\r?\n|\r))??\1/m,alias:"comment"},table:{pattern:/^\|={3,}(?:(?:\r?\n|\r(?!\n)).*)*?(?:\r?\n|\r)\|={3,}$/m,inside:{specifiers:{pattern:/(?:(?:(?:\d+(?:\.\d+)?|\.\d+)[+*](?:[<^>](?:\.[<^>])?|\.[<^>])?|[<^>](?:\.[<^>])?|\.[<^>])[a-z]*|[a-z]+)(?=\|)/,alias:"attr-value"},punctuation:{pattern:/(^|[^\\])[|!]=*/,lookbehind:!0}}},"passthrough-block":{pattern:/^(\+{4,})(?:\r?\n|\r)(?:[\s\S]*(?:\r?\n|\r))??\1$/m,inside:{punctuation:/^\++|\++$/}},"literal-block":{pattern:/^(-{4,}|\.{4,})(?:\r?\n|\r)(?:[\s\S]*(?:\r?\n|\r))??\1$/m,inside:{punctuation:/^(?:-+|\.+)|(?:-+|\.+)$/}},"other-block":{pattern:/^(--|\*{4,}|_{4,}|={4,})(?:\r?\n|\r)(?:[\s\S]*(?:\r?\n|\r))??\1$/m,inside:{punctuation:/^(?:-+|\*+|_+|=+)|(?:-+|\*+|_+|=+)$/}},"list-punctuation":{pattern:/(^[ \t]*)(?:-|\*{1,5}|\.{1,5}|(?:[a-z]|\d+)\.|[xvi]+\))(?= )/im,lookbehind:!0,alias:"punctuation"},"list-label":{pattern:/(^[ \t]*)[a-z\d].+(?::{2,4}|;;)(?=\s)/im,lookbehind:!0,alias:"symbol"},"indented-block":{pattern:/((\r?\n|\r)\2)([ \t]+)\S.*(?:(?:\r?\n|\r)\3.+)*(?=\2{2}|$)/,lookbehind:!0},comment:/^\/\/.*/m,title:{pattern:/^.+(?:\r?\n|\r)(?:={3,}|-{3,}|~{3,}|\^{3,}|\+{3,})$|^={1,5} .+|^\.(?![\s.]).*/m,alias:"important",inside:{punctuation:/^(?:\.|=+)|(?:=+|-+|~+|\^+|\++)$/}},"attribute-entry":{pattern:/^:[^:\r\n]+:(?: .*?(?: \+(?:\r?\n|\r).*?)*)?$/m,alias:"tag"},attributes:n,hr:{pattern:/^'{3,}$/m,alias:"punctuation"},"page-break":{pattern:/^<{3,}$/m,alias:"punctuation"},admonition:{pattern:/^(?:TIP|NOTE|IMPORTANT|WARNING|CAUTION):/m,alias:"keyword"},callout:[{pattern:/(^[ \t]*)<?\d*>/m,lookbehind:!0,alias:"symbol"},{pattern:/<\d+>/,alias:"symbol"}],macro:{pattern:/\b[a-z\d][a-z\d-]*::?(?:[^\s\[\]]*\[(?:[^\]\\"']|(["'])(?:(?!\1)[^\\]|\\.)*\1|\\.)*\])/,inside:{function:/^[a-z\d-]+(?=:)/,punctuation:/^::?/,attributes:{pattern:/(?:\[(?:[^\]\\"']|(["'])(?:(?!\1)[^\\]|\\.)*\1|\\.)*\])/,inside:n.inside}}},inline:{pattern:/(^|[^\\])(?:(?:\B\[(?:[^\]\\"']|(["'])(?:(?!\2)[^\\]|\\.)*\2|\\.)*\])?(?:\b_(?!\s)(?: _|[^_\\\r\n]|\\.)+(?:(?:\r?\n|\r)(?: _|[^_\\\r\n]|\\.)+)*_\b|\B``(?!\s).+?(?:(?:\r?\n|\r).+?)*''\B|\B`(?!\s)(?:[^`'\s]|\s+\S)+['`]\B|\B(['*+#])(?!\s)(?: \3|(?!\3)[^\\\r\n]|\\.)+(?:(?:\r?\n|\r)(?: \3|(?!\3)[^\\\r\n]|\\.)+)*\3\B)|(?:\[(?:[^\]\\"']|(["'])(?:(?!\4)[^\\]|\\.)*\4|\\.)*\])?(?:(__|\*\*|\+\+\+?|##|\$\$|[~^]).+?(?:(?:\r?\n|\r).+?)*\5|\{[^}\r\n]+\}|\[\[\[?.+?(?:(?:\r?\n|\r).+?)*\]?\]\]|<<.+?(?:(?:\r?\n|\r).+?)*>>|\(\(\(?.+?(?:(?:\r?\n|\r).+?)*\)?\)\)))/m,lookbehind:!0,inside:{attributes:n,url:{pattern:/^(?:\[\[\[?.+?\]?\]\]|<<.+?>>)$/,inside:{punctuation:/^(?:\[\[\[?|<<)|(?:\]\]\]?|>>)$/}},"attribute-ref":{pattern:/^\{.+\}$/,inside:{variable:{pattern:/(^\{)[a-z\d,+_-]+/,lookbehind:!0},operator:/^[=?!#%@$]|!(?=[:}])/,punctuation:/^\{|\}$|::?/}},italic:{pattern:/^(['_])[\s\S]+\1$/,inside:{punctuation:/^(?:''?|__?)|(?:''?|__?)$/}},bold:{pattern:/^\*[\s\S]+\*$/,inside:{punctuation:/^\*\*?|\*\*?$/}},punctuation:/^(?:``?|\+{1,3}|##?|\$\$|[~^]|\(\(\(?)|(?:''?|\+{1,3}|##?|\$\$|[~^`]|\)?\)\))$/}},replacement:{pattern:/\((?:C|TM|R)\)/,alias:"builtin"},entity:/&#?[\da-z]{1,8};/i,"line-continuation":{pattern:/(^| )\+$/m,lookbehind:!0,alias:"punctuation"}};function i(t){for(var n={},i=0,e=(t=t.split(" ")).length;i<e;i++)n[t[i]]=a[t[i]];return n}n.inside.interpreted.inside.rest=i("macro inline replacement entity"),a["passthrough-block"].inside.rest=i("macro"),a["literal-block"].inside.rest=i("callout"),a.table.inside.rest=i("comment-block passthrough-block literal-block other-block list-punctuation indented-block comment title attribute-entry attributes hr page-break admonition list-label callout macro inline replacement entity line-continuation"),a["other-block"].inside.rest=i("table list-punctuation indented-block comment attribute-entry attributes hr page-break admonition list-label macro inline replacement entity line-continuation"),a.title.inside.rest=i("macro inline replacement entity"),t.hooks.add("wrap",function(t){"entity"===t.type&&(t.attributes.title=t.content.replace(/&amp;/,"&"))}),t.languages.adoc=t.languages.asciidoc}(Prism);
\ No newline at end of file
diff --git a/components/prism-promql.js b/components/prism-promql.js
index 3a4504d..d78f00a 100644
--- a/components/prism-promql.js
+++ b/components/prism-promql.js
@@ -47,7 +47,7 @@
 			lookbehind: true,
 			inside: {
 				'label-key': {
-					pattern: /\b[^,]*\b/,
+					pattern: /\b[^,]+\b/,
 					alias: 'attr-name',
 				},
 				'punctuation': /[(),]/
diff --git a/components/prism-promql.min.js b/components/prism-promql.min.js
index 337aa9a..2a40ae6 100644
--- a/components/prism-promql.min.js
+++ b/components/prism-promql.min.js
@@ -1 +1 @@
-!function(t){var n=["on","ignoring","group_right","group_left","by","without"],a=["sum","min","max","avg","group","stddev","stdvar","count","count_values","bottomk","topk","quantile"].concat(n,["offset"]);t.languages.promql={comment:{pattern:/(^[ \t]*)#.*/m,lookbehind:!0},"vector-match":{pattern:new RegExp("((?:"+n.join("|")+")\\s*)\\([^)]*\\)"),lookbehind:!0,inside:{"label-key":{pattern:/\b[^,]*\b/,alias:"attr-name"},punctuation:/[(),]/}},"context-labels":{pattern:/\{[^{}]*\}/,inside:{"label-key":{pattern:/\b[a-z_]\w*(?=\s*(?:=|![=~]))/,alias:"attr-name"},"label-value":{pattern:/(["'`])(?:\\[\s\S]|(?!\1)[^\\])*\1/,greedy:!0,alias:"attr-value"},punctuation:/\{|\}|=~?|![=~]|,/}},"context-range":[{pattern:/\[[\w\s:]+\]/,inside:{punctuation:/\[|\]|:/,"range-duration":{pattern:/\b(?:\d+(?:[smhdwy]|ms))+\b/i,alias:"number"}}},{pattern:/(\boffset\s+)\w+/,lookbehind:!0,inside:{"range-duration":{pattern:/\b(?:\d+(?:[smhdwy]|ms))+\b/i,alias:"number"}}}],keyword:new RegExp("\\b(?:"+a.join("|")+")\\b","i"),function:/\b[a-z_]\w*(?=\s*\()/i,number:/[-+]?(?:(?:\b\d+(?:\.\d+)?|\B\.\d+)(?:e[-+]?\d+)?\b|\b(?:0x[0-9a-f]+|nan|inf)\b)/i,operator:/[\^*/%+-]|==|!=|<=|<|>=|>|\b(?:and|unless|or)\b/i,punctuation:/[{};()`,.[\]]/}}(Prism);
\ No newline at end of file
+!function(t){var n=["on","ignoring","group_right","group_left","by","without"],a=["sum","min","max","avg","group","stddev","stdvar","count","count_values","bottomk","topk","quantile"].concat(n,["offset"]);t.languages.promql={comment:{pattern:/(^[ \t]*)#.*/m,lookbehind:!0},"vector-match":{pattern:new RegExp("((?:"+n.join("|")+")\\s*)\\([^)]*\\)"),lookbehind:!0,inside:{"label-key":{pattern:/\b[^,]+\b/,alias:"attr-name"},punctuation:/[(),]/}},"context-labels":{pattern:/\{[^{}]*\}/,inside:{"label-key":{pattern:/\b[a-z_]\w*(?=\s*(?:=|![=~]))/,alias:"attr-name"},"label-value":{pattern:/(["'`])(?:\\[\s\S]|(?!\1)[^\\])*\1/,greedy:!0,alias:"attr-value"},punctuation:/\{|\}|=~?|![=~]|,/}},"context-range":[{pattern:/\[[\w\s:]+\]/,inside:{punctuation:/\[|\]|:/,"range-duration":{pattern:/\b(?:\d+(?:[smhdwy]|ms))+\b/i,alias:"number"}}},{pattern:/(\boffset\s+)\w+/,lookbehind:!0,inside:{"range-duration":{pattern:/\b(?:\d+(?:[smhdwy]|ms))+\b/i,alias:"number"}}}],keyword:new RegExp("\\b(?:"+a.join("|")+")\\b","i"),function:/\b[a-z_]\w*(?=\s*\()/i,number:/[-+]?(?:(?:\b\d+(?:\.\d+)?|\B\.\d+)(?:e[-+]?\d+)?\b|\b(?:0x[0-9a-f]+|nan|inf)\b)/i,operator:/[\^*/%+-]|==|!=|<=|<|>=|>|\b(?:and|unless|or)\b/i,punctuation:/[{};()`,.[\]]/}}(Prism);
\ No newline at end of file
diff --git a/package.json b/package.json
index afea480..2c51900 100755
--- a/package.json
+++ b/package.json
@@ -59,6 +59,7 @@
     "npm-run-all": "^4.1.5",
     "pump": "^3.0.0",
     "refa": "^0.9.1",
+    "regexp-ast-analysis": "^0.2.4",
     "regexpp": "^3.2.0",
     "scslre": "^0.1.6",
     "simple-git": "^1.107.0",
diff --git a/tests/pattern-tests.js b/tests/pattern-tests.js
index 282021a..5ebaaa6 100644
--- a/tests/pattern-tests.js
+++ b/tests/pattern-tests.js
@@ -12,6 +12,7 @@ const { transform, combineTransformers, getIntersectionWordSets, JS, Words, NFA,
 const scslre = require('scslre');
 const path = require('path');
 const { argv } = require('yargs');
+const RAA = require('regexp-ast-analysis');
 
 /**
  * A map from language id to a list of code snippets in that language.
@@ -130,6 +131,7 @@ function testPatterns(Prism, mainLanguage) {
 	 * @property {string} name
 	 * @property {any} parent
 	 * @property {boolean} lookbehind Whether the first capturing group of the pattern is a Prism lookbehind group.
+	 * @property {CapturingGroup | undefined} lookbehindGroup
 	 * @property {{ key: string, value: any }[]} path
 	 * @property {(message: string) => void} reportError
 	 */
@@ -163,6 +165,8 @@ function testPatterns(Prism, mainLanguage) {
 						}
 
 						const parent = path.length > 1 ? path[path.length - 2].value : undefined;
+						const lookbehind = key === 'pattern' && parent && !!parent.lookbehind;
+						const lookbehindGroup = lookbehind ? getFirstCapturingGroup(ast.pattern) : undefined;
 						callback({
 							pattern: value,
 							ast,
@@ -170,7 +174,8 @@ function testPatterns(Prism, mainLanguage) {
 							name: key,
 							parent,
 							path,
-							lookbehind: key === 'pattern' && parent && !!parent.lookbehind,
+							lookbehind,
+							lookbehindGroup,
 							reportError: message => errors.push(message)
 						});
 					} catch (error) {
@@ -231,9 +236,10 @@ function testPatterns(Prism, mainLanguage) {
 
 
 	it('- should not match the empty string', function () {
-		forEachPattern(({ pattern, tokenPath }) => {
+		forEachPattern(({ ast, pattern, tokenPath }) => {
 			// test for empty string
-			assert.notMatch('', pattern, `${tokenPath}: ${pattern} should not match the empty string.\n\n`
+			const empty = RAA.isPotentiallyZeroLength(ast.pattern.alternatives);
+			assert.isFalse(empty, `${tokenPath}: ${pattern} should not match the empty string.\n\n`
 				+ `Patterns that do match the empty string can potentially cause infinitely many empty tokens. `
 				+ `Make sure that all patterns always consume at least one character.`);
 		});
@@ -256,47 +262,37 @@ function testPatterns(Prism, mainLanguage) {
 	});
 
 	it('- should not have lookbehind groups that can be preceded by other some characters', function () {
-		forEachPattern(({ ast, tokenPath, lookbehind }) => {
-			if (!lookbehind) {
-				return;
+		forEachPattern(({ tokenPath, lookbehindGroup }) => {
+			if (lookbehindGroup && !isFirstMatch(lookbehindGroup)) {
+				assert.fail(`${tokenPath}: The lookbehind group ${lookbehindGroup.raw} might be preceded by some characters.\n\n`
+					+ `Prism assumes that the lookbehind group, if captured, is the first thing matched by the regex. `
+					+ `If characters might precede the lookbehind group (e.g. /a?(b)c/), then Prism cannot correctly apply the lookbehind correctly in all cases.\n`
+					+ `To fix this, either remove the preceding characters or include them in the lookbehind group.`);
 			}
-			forEachCapturingGroup(ast.pattern, ({ group, number }) => {
-				if (number === 1 && !isFirstMatch(group)) {
-					assert.fail(`${tokenPath}: The lookbehind group ${group.raw} might be preceded by some characters.\n\n`
-						+ `Prism assumes that the lookbehind group, if captured, is the first thing matched by the regex. `
-						+ `If characters might precede the lookbehind group (e.g. /a?(b)c/), then Prism cannot correctly apply the lookbehind correctly in all cases.\n`
-						+ `To fix this, either remove the preceding characters or include them in the lookbehind group.`);
-				}
-			});
 		});
 	});
 
 	it('- should not have lookbehind groups that only have zero-width alternatives', function () {
-		forEachPattern(({ ast, tokenPath, lookbehind, reportError }) => {
-			if (!lookbehind) {
-				return;
+		forEachPattern(({ tokenPath, lookbehindGroup, reportError }) => {
+			if (lookbehindGroup && RAA.isZeroLength(lookbehindGroup)) {
+				const groupContent = lookbehindGroup.raw.substr(1, lookbehindGroup.raw.length - 2);
+				const replacement = lookbehindGroup.alternatives.length === 1 ? groupContent : `(?:${groupContent})`;
+				reportError(`${tokenPath}: The lookbehind group ${lookbehindGroup.raw} does not consume characters.\n\n`
+					+ `Therefor it is not necessary to use a lookbehind group.\n`
+					+ `To fix this, replace the lookbehind group with ${replacement} and remove the 'lookbehind' property.`);
 			}
-			forEachCapturingGroup(ast.pattern, ({ group, number }) => {
-				if (number === 1 && isAlwaysZeroWidth(group)) {
-					const groupContent = group.raw.substr(1, group.raw.length - 2);
-					const replacement = group.alternatives.length === 1 ? groupContent : `(?:${groupContent})`;
-					reportError(`${tokenPath}: The lookbehind group ${group.raw} does not consume characters.\n\n`
-						+ `Therefor it is not necessary to use a lookbehind group.\n`
-						+ `To fix this, replace the lookbehind group with ${replacement} and remove the 'lookbehind' property.`);
-				}
-			});
 		});
 	});
 
 	it('- should not have unused capturing groups', function () {
-		forEachPattern(({ ast, tokenPath, lookbehind, reportError }) => {
+		forEachPattern(({ ast, tokenPath, lookbehindGroup, reportError }) => {
 			forEachCapturingGroup(ast.pattern, ({ group, number }) => {
-				const isLookbehindGroup = lookbehind && number === 1;
+				const isLookbehindGroup = group === lookbehindGroup;
 				if (group.references.length === 0 && !isLookbehindGroup) {
 					const fixes = [];
 					fixes.push(`Make this group a non-capturing group ('(?:...)' instead of '(...)'). (It's usually this option.)`);
 					fixes.push(`Reference this group with a backreference (use '\\${number}' for this).`);
-					if (number === 1 && !lookbehind) {
+					if (number === 1 && !lookbehindGroup) {
 						if (isFirstMatch(group)) {
 							fixes.push(`Add a 'lookbehind: true' declaration.`);
 						} else {
@@ -392,28 +388,26 @@ function testPatterns(Prism, mainLanguage) {
 
 
 /**
- * Returns whether the given element will always have zero width meaning that it doesn't consume characters.
+ * Returns the first capturing group in the given pattern.
  *
- * @param {Element} element
- * @returns {boolean}
+ * @param {Pattern} pattern
+ * @returns {CapturingGroup | undefined}
  */
-function isAlwaysZeroWidth(element) {
-	switch (element.type) {
-		case 'Assertion':
-			// assertions == ^, $, \b, lookarounds
-			return true;
-		case 'Quantifier':
-			return element.max === 0 || isAlwaysZeroWidth(element.element);
-		case 'CapturingGroup':
-		case 'Group':
-			// every element in every alternative has to be of zero length
-			return element.alternatives.every(alt => alt.elements.every(isAlwaysZeroWidth));
-		case 'Backreference':
-			// on if the group referred to is of zero length
-			return isAlwaysZeroWidth(element.resolved);
-		default:
-			return false; // what's left are characters
+function getFirstCapturingGroup(pattern) {
+	let cap = undefined;
+
+	try {
+		visitRegExpAST(pattern, {
+			onCapturingGroupEnter(node) {
+				cap = node;
+				throw new Error('stop');
+			}
+		});
+	} catch (error) {
+		// ignore errors
 	}
+
+	return cap;
 }
 
 /**
@@ -427,7 +421,7 @@ function isFirstMatch(element) {
 	switch (parent.type) {
 		case 'Alternative': {
 			// all elements before this element have to of zero length
-			if (!parent.elements.slice(0, parent.elements.indexOf(element)).every(isAlwaysZeroWidth)) {
+			if (!parent.elements.slice(0, parent.elements.indexOf(element)).every(RAA.isZeroLength)) {
 				return false;
 			}
 			const grandParent = parent.parent;
@@ -457,13 +451,7 @@ function isFirstMatch(element) {
  * @returns {boolean}
  */
 function underAStar(node) {
-	if (node.type === 'Quantifier' && node.max > 10) {
-		return true;
-	} else if (node.parent) {
-		return underAStar(node.parent);
-	} else {
-		return false;
-	}
+	return RAA.getEffectiveMaximumRepetition(node) > 10;
 }
 
 /**